#include <bits/stdc++.h>

using namespace std;
int dfs(int u) {
    if (u == 1) return 0;
    if (u == 2) return 1;
    return dfs(u - 1) + dfs(u - 2);
}
int main() {
    int n;
    cin >> n;
    cout << dfs(n+1) << endl;
    return 0;
}