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

/**************************************************************
	Problem: 1052
	User: tangkaixuan
	Language: C++
	Result: Wrong Answer
****************************************************************/