#include<bits/stdc++.h>
using namespace std;
int main(){
	;
	float a,b;
	cin>>a;
	if(a>1.5*10){
		b=(a-15)/2.5+10;
	}else if(a<=1.5*10){
		b=a/1.5;	
	}
	printf("%.2f",b);
}
/**************************************************************
	Problem: 1052
	User: toughuatao1
	Language: C++
	Result: Accepted
	Time:9 ms
	Memory:2072 kb
****************************************************************/