#include<bits/stdc++.h> using namespace std; int main() { double n; cin>>n; if (0 <= n < 5){ printf("%.3lf",-n+2.5); } else if( 5 <= n < 10 ){ printf("%.3lf",2-1.5*(n-3)*(n-3)); } else{ printf("%.3lf",n/2-1.5); } return 0; }