#include<bits/stdc++.h>
using namespace std;
int main() {
	int n;
	cin>>n;
	if(n>1.5*10) printf("%.2f",(n-1.5*10)/2.5+10); 
	else printf("%.2f",n/1.5);
	
}
/**************************************************************
	Problem: 1052
	User: linzihang
	Language: C++
	Result: Accepted
	Time:11 ms
	Memory:2072 kb
****************************************************************/