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#include <iostream>
using namespace std;

const int MAX = 202000;

int main() {
	int ctr[MAX] = {0};
	int n;
	cin >> n;

	while(n--) {
		int k;
		cin >> k;
		ctr[k]++;
	}

	int result = 0;

	for(int i = 0; i < MAX - 1; i++) {
		if(ctr[i] >= 1) {
			result = i;
		}

		int r = ctr[i] / 2;
		if(r >= 1) {
			ctr[i+1] += r;
		}
	}

	cout << result;
	return 0;
}