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#include <iostream>
using namespace std;

const int AI_MAX = 201718 + 21 + 1;

int b[AI_MAX];

int n;

int main () {
	for (int i = 0; i < AI_MAX; i++) {
		b[i] = 0;
	}

	cin >> n;
	int ai;
	for (int i = 0; i < n; i++) {
		cin >> ai;
		b[ai]++;
	}
			
	for (int i = 1; i < AI_MAX; i++) {
		b[i] += b[i-1] / 2;
	}

	for (int i = AI_MAX-1; i >= 0; i--) {
		if (b[i] != 0) {
			cout << i << endl;
			break;
		}
	}
	
	return 0;
}