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#include <cstdio>

#define N 202000

int t[N + 10];

int main () {
	int n, a;
	
	scanf("%d", &n);
	
	for (int i = 0; i < n; i++) {
		scanf("%d", &a);
		
		t[a]++;
	}
	
	for (int i = 0; i < N; i++) {
		a = t[i];
		
		t[i] = a % 2;
		t[i + 1] += a / 2;
	}
	
	for (int i = N - 1; i >= 0; i--) {
		if (t[i] != 0) {
			printf("%d", i);
			
			break;
		}
	}
	
	return 0;
}