#include<bits/stdc++.h>
using namespace std;
int main(){
    double a,ans;
    cin>>a;
    if(a<=10){
        ans=2.5;
    }
    else{
        ans=2.5+(a-10)*1.5;
    }
    printf("%.2f",ans);
}
 
/**************************************************************
	Problem: 1043
	User: panjinyan
	Language: C++
	Result: Accepted
	Time:26 ms
	Memory:2072 kb
****************************************************************/