#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: zhuangsongyu
	Language: C++
	Result: Accepted
	Time:13 ms
	Memory:2072 kb
****************************************************************/