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#include <bits/stdc++.h>

using namespace std;

const int N = 500000;

int cnt[N];
int n, x;

int main() {
    
    scanf("%d", &n);
    int mx = 0;
    for (int i = 1; i <= n; i++) {
        scanf("%d", &x);
        cnt[x]++;
        mx = max(mx, x);
    }
    
    int ans = 0;
    for (int i = 0; i <= mx + 50; i++) {
        cnt[i + 1] += cnt[i] / 2;
        cnt[i] %= 2;
        if (cnt[i] > 0) {
            ans = i;
        }
    }
    
    printf("%d\n", ans);
    
    return 0;
}