#include <cstdio>
#include <cmath>
using namespace std;
int main() {
	int k, m = 1, n = 1, sum, t;
	scanf("%d", &t);
	for (int i = 1; i <= t; ++i) {
		scanf("%d", &k);
		for (int j = 1; j <= k ; ++i) {
			if (j == 1 || j == 2) {
				sum = 1;
				continue;
			}
			sum = m + n;
			m = n;
			n = sum;
		}
	}
	printf("%d", sum);
	return 0;
}