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#include <stdio.h>

int main() {
    const int MAX_DELTA = 20;
    const int MAX_NOMINAL = 201718 + MAX_DELTA;
    int n;
    int nominals[MAX_NOMINAL + 1] = {};
    int max_nominal = 0;

    scanf("%d", &n);

    for (int i = 0; i < n; i++) {
        int a;
        scanf("%d", &a);
        nominals[a]++;
    }

    for (int i = 0; i < MAX_NOMINAL + 1; i++) {
        int power = 1;
        if (nominals[i] & 1) {
            max_nominal = i;
        }
        nominals[i] >>= 1;
        while (nominals[i]) {
            if (nominals[i] & 1) {
                nominals[i + power]++;
            }
            nominals[i] >>= 1;
            power++;
        }
    }

    printf("%d", max_nominal);

    return 0;
};