#include <bits/stdc++.h>
using namespace std;
const int N = 1e5 + 6;
int n, f[N];
int main() {
	scanf("%d", &n);
	if (n <= 2) {
	    printf("1");
	    return 0;
	}
	f[1] = 1;
	f[2] = 2;
	for (int i = 3; i <= n; ++i)
	    f[i] = f[i - 1] + f[i - 2];
	printf("%d", f[n - 1]);
	return 0;
}