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#include <cstdio>

int main() {
	int a[201739];
	for (int i = 0; i < 201739; i++) {
		a[i] = 0;
	}
	int n;
	int ai;
	scanf("%d", &n);
	for (int i = 0; i < n; i++) {
		scanf("%d", &ai);
		a[ai]++;
	}
	int carry = 0;
	for (int i = 0; i < 201739; i++) {
		a[i] += carry;
		if (a[i] > 1) {
			if ((a[i] & 1) == 0) {
				carry = a[i];
				a[i] = 0;
			}
			else {
				carry = a[i] - 1;
				a[i] = 1;
			}
		}
		carry /= 2;
	}
	for (int i = 201738; i >= 0; i--) {
		if (a[i] > 0) {
			printf("%d\n", i);
			break;
		}
	}
	return 0;
}