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#include <iostream>

int tab[201740];

int main() {
    std::ios_base::sync_with_stdio(0);

    int n, ma = 0;
    std::cin >> n;
    for (int i = 0; i < n; i++) {
        int a;
        std::cin >> a;
        tab[a]++;
        if (ma < a)
            ma = a;
    }

    int i = 0;
    int prev = 0;
    while (i <= ma || prev > 0) {
        prev += tab[i];
        prev >>= 1;
        i++;
    }

    std::cout << i - 1;
}