Polycarpus adores TV series. Right now he is ready to finish watching a season of a popular sitcom "Graph Theory". In total, the season has *n* episodes, numbered with integers from 1 to *n*.

Polycarpus watches episodes not one by one but in a random order. He has already watched all the episodes except for one. Which episode has Polycaprus forgotten to watch?
The first line of the input contains integer *n* (2 ≤ *n* ≤ 100000) — the number of episodes in a season. Assume that the episodes are numbered by integers from 1 to *n*.

The second line contains *n* - 1 integer *a*<sub class="lower-index">1</sub>, *a*<sub class="lower-index">2</sub>, ..., *a*<sub class="lower-index">*n*</sub> (1 ≤ *a*<sub class="lower-index">*i*</sub> ≤ *n*) — the numbers of episodes that Polycarpus has watched. All values of *a*<sub class="lower-index">*i*</sub> are distinct.
'''
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// •︿• \\
/\\    //\
 /\\  //\
  /\\//\

###########################
'''
import sys
import math as mth
from math import ceil as cl
from math import log2 as l2
from math import factorial as fct
from collections import Counter as CNT
from math import log
from math import floor as fl
mod = 10**9 + 7
months = ['January', 'February', 'March', 'April', 'May', 'June', 'July', 'August', 'September', 'October', 'November', 'December']
alp = ['a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j', 'k', 'l', 'm', 'n', 'o', 'p', 'q', 'r', 's', 't', 'u', 'v', 'w', 'x', 'y', 'z']
def ii():
    return int(input())
def fi():
    return float(input())
def lii():
    return list(map(int, input().split()))
def ss():
    return input()
def lss():
    return input().split()
def yes():
    print("YES")
def no():
    print("NO")
############################################
input = lambda : sys.stdin.readline().strip()
'''
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'''
n = ii()
arr = sorted(lii())
print(((n*(n+1))//2)-sum(arr))