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#include <iostream>
#include <algorithm>

int main() {
    std::ios_base::sync_with_stdio(false);
    std::cin.tie(NULL);
    unsigned n;
    std::cin >> n;
    const int SIZE = 201720 + 50;
    auto * coins = new unsigned[SIZE];
    std::fill(coins, coins + SIZE, 0);
    for (int i = 0; i < n; ++i) {
        unsigned long long coin;
        std::cin >> coin;
        coins[coin]++;
    }
    for (int i = 0; i < SIZE - 1; i++)
        coins[i + 1] += coins[i] / 2;

    for (int i = SIZE - 1; i >= 0; i--) {
        if (coins[i]) {
            std::cout << i << std::endl;
            break;
        }
    }
}