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#include <bits/stdc++.h>
using namespace std;

int n;
int t[1000006];

int main(){
	scanf("%d", &n);
	int maks = 0;
	for (int i = 1; i <= n; ++i){
		int a;scanf("%d", &a);
		maks = max(maks,a);
		++t[a];
	}
	for (int i = 0; i <= 1000000; ++i){
		if (t[i] == 0 && i > maks)
			break;
		if (t[i] == 1 && i >= maks){
			printf("%d\n", i);
			return 0;
		}
		t[i + 1] += t[i] / 2;
	}

}