#include<bits/stdc++.h>
using namespace std;
int main(){
    double a,ans;
    cin>>a;
    if(a<=10*1.5){
        ans=a/1.5;
    }
    else{
        ans=10+(a-15)/2.5;
    }
    printf("%.2f",ans);
}
/**************************************************************
	Problem: 1052
	User: wangchenyu
	Language: C++
	Result: Accepted
	Time:10 ms
	Memory:2072 kb
****************************************************************/