#include<bits/stdc++.h>
using namespace std;
int main(){
	float x,p,a,b;
	cin>>x;
	a=x*0.8;
	b=x*0.9;
	p=(x+a+b)/3.0;
	printf("%.1f",p);
	return 0;
}


/**************************************************************
	Problem: 1613
	User: huangcanwu
	Language: C++
	Result: Accepted
	Time:7 ms
	Memory:2072 kb
****************************************************************/