#include<iostream>
#include<iomanip>
using namespace std;
int main(){
    double g =0.0;
    int q = 2.5;
    if(g <= 10){
   	    q = q*1;   
   }eles{
        q = (g-10 )*2.5;  	
   }
	cout << fixed << setprecision(2)<<q<<endl;
}