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#include <cstdio>
#include <algorithm>

using namespace std;

const int MAXA = 1 << 19;

int c[MAXA + 1];

int main() {

    int n, a;

    scanf("%d", &n);

    for (int i = 0; i < n; ++i) {

        scanf("%d", &a);

        c[a]++;
    }

    int ans = 0;

    for (int i = 0; i < MAXA; ++i) {

        if (c[i] > 0)
            ans = i;

        c[i + 1] += c[i] / 2;
    }

    printf("%d\n", ans);
}