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#include <cstdio>

using namespace std;

const int MAX_POW = 201718;

int pow_occ[MAX_POW+1];

int main() {

    int n;
    scanf("%d", &n);

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

    int max_pow = -1, curr_pow = 1, acc = 0;

    for(; curr_pow <= MAX_POW; curr_pow++) {
        acc /= 2;
        acc += pow_occ[curr_pow];
        if(acc != 0) max_pow = curr_pow;
    }

    while(true) {
        acc /= 2;
        if(acc == 0)
            break;
        max_pow = curr_pow;
        curr_pow++;
    }

    printf("%d\n", max_pow);

    return 0;
}