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#include <bits/stdc++.h>
using namespace std;
#define ff first
#define dd second
#define mp make_pair
#define pb push_back
#define sz size()
#define lld long long
#define scanf(...) scanf(__VA_ARGS__)?:0
#define For(i,s,a) for(lld i=(lld)s;i<(lld)a;++i)

int c[1000001];

int main()
{
	int a,b;
	scanf("%d", &a);
	For(i,0,a)scanf("%d", &b),++c[b];
	b=0;
	For(i,0,1000000){
	b=(c[i])?i:b;
	c[i+1]+=c[i]>>1;}
	printf("%d",b);
}