#include<bits/stdc++.h>
using namespace std;
int main()
{
	float x,y,z;
	float n;
	cin>>x;
	y=x*0.8;
	z=x*0.9;
	n=(x+y+z)/3.0;
	printf("%.1f",n);
} 
/**************************************************************
	Problem: 1613
	User: tangkaixuan
	Language: C++
	Result: Accepted
	Time:8 ms
	Memory:2072 kb
****************************************************************/