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#include<cstdio>


const int MAX_POW = 300 * 1000;

int tab[MAX_POW];

int main() {
    int n, a;
    scanf("%d", &n);

    while(n--) {
        scanf("%d", &a);
        tab[a]++;
    }

    int best = 0;
    for (int i = 0; i < MAX_POW; ++i) {
        if (tab[i]) {
            best = i;
        }
        tab[i+1] += tab[i] / 2;
    }

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