#include<bits/stdc++.h>
using namespace std;
int main(){
	int x;
	float p=0,s=0,e=0;
	cin>>x;
	e=x*0.8;
    s=x*0.9;
	p=(x+e+s)/3;
	printf("%.1lf",p);
    }

/**************************************************************
	Problem: 1613
	User: huxuanchen
	Language: C++
	Result: Accepted
	Time:8 ms
	Memory:2072 kb
****************************************************************/