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#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <iostream>
#include <algorithm>
typedef long long ll;
const int N = 2.5e5 + 5;
using namespace std;


int n, x, ans, a[N];
int main() {
	for (scanf("%d", &n); n; n--) {
		scanf("%d", &x);
		a[x]++;
	}
	for (int i = 0; i < N - 5; i++) {
		a[i + 1] += a[i] / 2;
		if (a[i]) ans = i;
	}
	printf("%d\n", ans);
}