Ivan has got an array of n non-negative integers a1, a2, ..., an. Ivan knows that the array is sorted in the non-decreasing order. 

Ivan wrote out integers 2a1, 2a2, ..., 2an on a piece of paper. Now he wonders, what minimum number of integers of form 2b (b ≥ 0) need to be added to the piece of paper so that the sum of all integers written on the paper equalled 2v - 1 for some integer v (v ≥ 0). 

Help Ivan, find the required quantity of numbers.

Input

The first line contains integer n (1 ≤ n ≤ 105). The second input line contains n space-separated integers a1, a2, ..., an (0 ≤ ai ≤ 2·109). It is guaranteed that a1 ≤ a2 ≤ ... ≤ an.

Output

Print a single integer — the answer to the problem.

Examples

Input

4
0 1 1 1


Output

0


Input

1
3


Output

3

Note

In the first sample you do not need to add anything, the sum of numbers already equals 23 - 1 = 7.

In the second sample you need to add numbers 20, 21, 22.
#include <bits/stdc++.h>
using namespace std;
int n;
set<long long> S;
set<long long> num;
long long tem;
long long maxx;
inline void oper(long long x) {
  if (!num.count(tem)) {
    num.insert(tem);
  }
}
int main() {
  while (scanf("%d", &n) == 1) {
    maxx = 0;
    S.clear();
    num.clear();
    while (n--) {
      scanf("%I64d", &tem);
      while (S.count(tem)) {
        S.erase(tem);
        tem++;
      }
      maxx = max(maxx, tem);
      S.insert(tem);
      oper(tem);
    }
    printf("%I64d\n", maxx - S.size() + 1);
  }
}
