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

const int maxn = 1<<20;
int n, x, t[maxn];

int main () {
	scanf("%d", &n);
	for (int i = 1; i <= n; i++) {
		scanf("%d", &x);
		t[x]++;
	}
	for (int i = 0; i < maxn - 1; i++) {
		t[i + 1] += t[i] / 2;
		t[i] &= 1;
	}
	int res = maxn - 1;
	while (t[res] == 0)
		res--;
	printf("%d\n", res); 
	return 0;
}