#include<cstdio>
int main() {
	int n;
	while(scanf("%d", &n) != EOF) {
		int f1 = 1, f2 = 2;
		for(int i = 2; i < n; i++){
			int tmp = f1;
			f1 = f2;
			f2 += tmp;
		}
		if(n == 1) printf("%d\n", 1);
		else printf("%d\n", f2);
	}
}