#include<bits/stdc++.h>
using namespace std;
int main(){
	float a,p;
	cin>>a;
	if (a<=15){
		p=a/1.5;
		printf("%.2f",p);
	}
	else {
		p=10+(a-15)/2.5;
		printf("%.2f",p);
	}
	return 0;
}
/**************************************************************
	Problem: 1052
	User: xiaojingxuan
	Language: C++
	Result: Accepted
	Time:8 ms
	Memory:2072 kb
****************************************************************/