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#include <map>
#include <vector>

static const int LOG_ONE_MILION = 20;

static const int MAX = 201718;

int main() {
    int count;
    int number;

    scanf("%d", &count);

    std::vector<int> v(MAX + LOG_ONE_MILION + 2);

    for (auto i = 0; i < count; i++) {
        scanf("%d", &number);
        v[number]++;
    }

    int best = 0;

    for (auto i = 0; i < MAX + LOG_ONE_MILION + 1; i++) {
        v[i + 1] += v[i] / 2;
        if (v[i] > 0) {
            best = i;
        }
    }

    printf("%d\n", best);
    return 0;
}