#include<bits/stdc++.h>
using namespace std;
int main(){
	int n;
	float a,s,d;
	cin>>n;
	a=(n-15)/2.5;
	s=n/1.5;
	d=10+a;
	if(n<=15){
		printf("%.2f",s);
	}if(n>15){
		printf("%.2f",d);
	}	
}
/**************************************************************
	Problem: 1052
	User: sucongyi
	Language: C++
	Result: Accepted
	Time:8 ms
	Memory:2072 kb
****************************************************************/