Little penguin Polo has an *n* × *m* matrix, consisting of integers. Let's index the matrix rows from 1 to *n* from top to bottom and let's index the columns from 1 to *m* from left to right. Let's represent the matrix element on the intersection of row *i* and column *j* as *a*<sub class="lower-index">*ij*</sub>.

In one move the penguin can add or subtract number *d* from some matrix element. Find the minimum number of moves needed to make all matrix elements equal. If the described plan is impossible to carry out, say so.
The first line contains three integers *n*, *m* and *d* (1 ≤ *n*, *m* ≤ 100, 1 ≤ *d* ≤ 10<sup class="upper-index">4</sup>) — the matrix sizes and the *d* parameter. Next *n* lines contain the matrix: the *j*-th integer in the *i*-th row is the matrix element *a*<sub class="lower-index">*ij*</sub> (1 ≤ *a*<sub class="lower-index">*ij*</sub> ≤ 10<sup class="upper-index">4</sup>).
# DEFINING SOME GOOD STUFF
import sys
from math import *
import threading
from itertools import count
from pprint import pprint
from collections import defaultdict
'''
    intialise defaultdict by any kind of value by default you want to take ( int -> 0 | list -> [] )
'''
from heapq import heapify, heappop, heappush
sys.setrecursionlimit(300000)
# threading.stack_size(10**8)
'''
-> if you are increasing recursionlimit then remember submitting using python3 rather pypy3
-> sometimes increasing stack size don't work locally but it will work on CF
'''

mod = 10 ** 9 + 7
inf = 10 ** 15
decision = ['NO', 'YES']
yes = 'YES'
no = 'NO'

# ------------------------------FASTIO----------------------------
import os

from io import BytesIO, IOBase

BUFSIZE = 8192


class FastIO(IOBase):
    newlines = 0

    def __init__(self, file):
        self._fd = file.fileno()
        self.buffer = BytesIO()
        self.writable = "x" in file.mode or "r" not in file.mode
        self.write = self.buffer.write if self.writable else None

    def read(self):
        while True:
            b = os.read(self._fd, max(os.fstat(self._fd).st_size, BUFSIZE))
            if not b:
                break
            ptr = self.buffer.tell()
            self.buffer.seek(0, 2), self.buffer.write(b), self.buffer.seek(ptr)
        self.newlines = 0
        return self.buffer.read()

    def readline(self):
        while self.newlines == 0:
            b = os.read(self._fd, max(os.fstat(self._fd).st_size, BUFSIZE))
            self.newlines = b.count(b"\n") + (not b)
            ptr = self.buffer.tell()
            self.buffer.seek(0, 2), self.buffer.write(b), self.buffer.seek(ptr)
        self.newlines -= 1
        return self.buffer.readline()

    def flush(self):
        if self.writable:
            os.write(self._fd, self.buffer.getvalue())
            self.buffer.truncate(0), self.buffer.seek(0)


class IOWrapper(IOBase):
    def __init__(self, file):
        self.buffer = FastIO(file)
        self.flush = self.buffer.flush
        self.writable = self.buffer.writable
        self.write = lambda s: self.buffer.write(s.encode("ascii"))
        self.read = lambda: self.buffer.read().decode("ascii")
        self.readline = lambda: self.buffer.readline().decode("ascii")


sys.stdin, sys.stdout = IOWrapper(sys.stdin), IOWrapper(sys.stdout)
input = lambda: sys.stdin.readline().rstrip("\r\n")



# _______________________________________________________________#

def npr(n, r):
    return factorial(n) // factorial(n - r) if n >= r else 0


def ncr(n, r):
    return factorial(n) // (factorial(r) * factorial(n - r)) if n >= r else 0


def lower_bound(li, num):
    answer = -1
    start = 0
    end = len(li) - 1

    while (start <= end):
        middle = (end + start) // 2
        if li[middle] >= num:
            answer = middle
            end = middle - 1
        else:
            start = middle + 1
    return answer  # min index where x is not less than num


def upper_bound(li, num):
    answer = -1
    start = 0
    end = len(li) - 1

    while (start <= end):
        middle = (end + start) // 2

        if li[middle] <= num:
            answer = middle
            start = middle + 1

        else:
            end = middle - 1
    return answer  # max index where x is not greater than num


def abs(x):
    return x if x >= 0 else -x


def binary_search(li, val):
    # print(lb, ub, li)
    ans = -1
    lb = 0
    ub = len(li) - 1
    while (lb <= ub):
        mid = (lb + ub) // 2
        # print('mid is',mid, li[mid])
        if li[mid] > val:
            ub = mid - 1
        elif val > li[mid]:
            lb = mid + 1
        else:
            ans = mid  # return index
            break
    return ans


def kadane(x):  # maximum sum contiguous subarray
    sum_so_far = 0
    current_sum = 0
    for i in x:
        current_sum += i
        if current_sum < 0:
            current_sum = 0
        else:
            sum_so_far = max(sum_so_far, current_sum)
    return sum_so_far


def pref(li):
    pref_sum = [0]
    for i in li:
        pref_sum.append(pref_sum[-1] + i)
    return pref_sum


def SieveOfEratosthenes(n):
    prime = [True for i in range(n + 1)]
    p = 2
    li = []
    while (p * p <= n):
        if (prime[p] == True):
            for i in range(p * p, n + 1, p):
                prime[i] = False
        p += 1

    for p in range(2, len(prime)):
        if prime[p]:
            li.append(p)
    return li


def primefactors(n):
    factors = []
    while (n % 2 == 0):
        factors.append(2)
        n //= 2
    for i in range(3, int(sqrt(n)) + 1, 2):  # only odd factors left
        while n % i == 0:
            factors.append(i)
            n //= i
    if n > 2:  # incase of prime
        factors.append(n)
    return factors


def prod(li):
    ans = 1
    for i in li:
        ans *= i
    return ans


# _______________________________________________________________#


# def main():
for _ in range(1):
# for _ in range(int(input())):
#     n = int(input())
    n, m, d = map(int, input().split())
    # w, b = map(int, input().split())
    # a = list(map(int, input().split()))
    # b = list(map(int, input().split()))
    # c = list(map(int, input().split()))
    # d = defaultdict(int)
    a = []
    for i in range(n):
        a += list(map(int, input().split()))
    a.sort()
    elem = a[(n*m)//2]
    f = 0
    ans = 0
    for i in range(n*m):
        if abs(a[i] - elem)%d:
            f = 1
        ans += abs(a[i] - elem)
    if f:
        print(-1)
    else:
        print(ans//d)























































# t = threading.Thread(target=main)
# t.start()
# t.join()