#include<bits/stdc++.h>
using namespace std;
int main(){
	float n,z;
	cin>>n;
	if(n>15){
		z=(n-15)/2.5+10;
	}else{
		z=n/1.5;
	}
	printf("%.2f",z);
	return 0;
}

/**************************************************************
	Problem: 1052
	User: tangkaixuan
	Language: C++
	Result: Accepted
	Time:8 ms
	Memory:2072 kb
****************************************************************/