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#include <cstdio>

using namespace std;

const int MAXN = 1000005;
int a[MAXN];
int n;

int main() {
	scanf("%d", &n);
	for(int i=1; i<=n; i++) {
		int x;
		scanf("%d", &x);
		a[x]++;
	}

	int result = 0;

	for(int i=0; i<MAXN-1; i++) {
		if(a[i] > 0) result = i;

		int p = a[i]/2;
		a[i] -= p*2;
		a[i+1] += p;
	}

	printf("%d\n", result);

	return 0;
}