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#include <cstdio>

const int MAXA = 201718 + 5;
int n;
int m[MAXA];

int main() {
    scanf("%d", &n);
    int a;
    while(n--) {
        scanf("%d", &a);
        m[a]++;
    }
    for (size_t i = 1; i < MAXA; ++i) {
        m[i] += m[i - 1] / 2;
        m[i - 1] = m[i - 1] % 2;
    }
    for (size_t i = MAXA - 1; i >= 0; i--) {
        if (m[i] > 0) {
            printf("%d\n", i);
            return 0;
        }
    }
}