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#include<cstdio>
#include<vector>

using namespace std;

int main() {
    long n;
    scanf("%ld\n", &n);
    vector<long> coins(n);
    long max_val = 0l;
    for (long i = 0; i < n; i++) {
	scanf("%ld", &coins[i]);
	if (coins[i] > max_val) {
	    max_val = coins[i];
	}
    }

    vector<long> buckets(max_val + 1, 0);
    for (long i = 0; i < n; i++) {
	buckets[coins[i]]++;
    }

    for (long i = 0; i < max_val; i++) {
	long h_coins_num = buckets[i] / 2;
	buckets[i + 1] += h_coins_num;
	buckets[i] -= h_coins_num * 2;
    }

    long i = max_val;
    while (i >= 0 && buckets[i] == 0) {
	i--;
    }

    long result = 0l;
    if (i >= 0) {
	long coin_val = i;
	long coin_num = buckets[i];
	while (coin_num > 1) {
	    coin_num /= 2;
	    coin_val++;
	}
	result = coin_val;
    }

    printf("%ld\n", result);
    return 0;
}