#include <bits/stdc++.h> using namespace std; int main() { int n,fb,fb1=1,fb2=1; cin >> n; if(n==2||n==3) { cout << "1"; } else if(n==1) { cout <<"0"; } else { for(int i=4;i<=n;i++) { fb = fb1+fb2; fb1=fb2; fb2=fb; } cout << fb; } return 0; }