#include <bits/stdc++.h>
using namespace std;
int main() {
	float a,b;
	cin>>a;
	if(a<=15){
	b=a/1.5;
	}else{
	b=(a-2.5)/1.5;
	}
	printf("%.2f",b);
    return 0;
}
/**************************************************************
	Problem: 1052
	User: fuhoubin
	Language: C++
	Result: Wrong Answer
****************************************************************/