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#include <stdio.h>

using namespace std;

#define FOR0(i, n) for (int i = 0; i < n; i++)
#define FOR1(i, n) for (int i = 1; i < n; i++)
#define M 201719

int n;
int A[M];

int main() {
	scanf("%d", &n);
	int tmp, max = 0;
	FOR0(i, n) {
		scanf("%d", &tmp);
		A[tmp]++;
		if (max < tmp) max = tmp;
	}

	FOR1(i, max + 1) {
		A[i] += A[i - 1] / 2;
	}
	
	int counter = A[max];
	while (counter > 1) {
		counter /= 2;
		max++;
	}
	
	printf("%d\n", max);
	return 0;
}