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#include <bits/stdc++.h>

const int MAXA = 300000;

using namespace std;

int n, t[MAXA];

int main() {
    ios_base::sync_with_stdio(0);
    cin.tie(0);

    cin >> n;

    for (int i = 0; i < n; i++) {
        int x;
        cin >> x;
        t[x]++;
    }

    int res = -1;
    for (int i = 0; i + 1 < MAXA; i++) {
        if (t[i]) {
            res = i;
            t[i + 1] += t[i] / 2;
            t[i] = t[i] & 1;
        }
    }

    cout << res << "\n";
}