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#include <iostream>
#include <array>
using namespace std;
using u32 = unsigned int;




int main() {
    u32 n;
    cin >> n;

    array<u32, 201718 + 1> coins {0};

    for (u32 i = 0; i < n; ++i) {
        u32 c;
        cin >> c;
        coins[c]++;
    }


    for (u32 i = 0; i < coins.size() - 1; ++i) {
        u32 pairs = coins[i] / 2;  // each pair can be exchanged for 1 bigger coin
        coins[i+1] += pairs;
    }


    u32 max_val = 0;
    for (u32 i = 0; i < coins.size(); ++i) {
        if (coins[i] > 0)
            max_val = i;
    }


    cout << max_val << "\n";

    return 0;
}