#include<bits/stdc++.h>
using namespace std;
int main(){
    double x,y;
    cin>>x;
    if(x<5) y=(-x)+2.5;
    else if(x<=5 && x<10) y=2.0-1.5*(x-3)*(x-3);
    else y=x/2.0-1.5;
    printf("%.3lf",y);
    return 0;
}