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#include <cstdio>
#include <iostream>
#include <algorithm>
using namespace std;

long long int tab[500000];
long long int wyn[500000];

int main() {
	ios_base::sync_with_stdio(0);
	int n, a, maxx = 0;
	cin >> n;
	for(int i = 1; i <= n; i++) {
		cin >> a;
		tab[a]++;
		maxx = max(maxx, a);
	}
	int x = 1;
	while(x <= maxx) {
		wyn[x] = tab[x] + (wyn[x-1]/2);
		if(wyn[x] > 1) {
			maxx = max(maxx, x+1);
		}
		x++;
	}
	cout << maxx;
	
	return 0;
}