#include<bits/stdc++.h>
using namespace std;
int main(){
    int n;
    float x;
    cin>>n;
    if(n<=10){
        x=2.5;
        printf("%.2f",x);
    }else{
        x=2.5+(n-10)*1.5;
        printf("%.2f",x);
    }
}
/**************************************************************
	Problem: 1043
	User: baizhoudeyueguang
	Language: C++
	Result: Accepted
	Time:18 ms
	Memory:2072 kb
****************************************************************/