#include<bits/stdc++.h>
using namespace std;
int main()
{
	int n;
	cin>>n;
	cout<<fixed<<setprecision(1)<<(n+n*0.8+n*0.9) / 3;
}

/**************************************************************
	Problem: 1613
	User: admin
	Language: C++
	Result: Accepted
	Time:11 ms
	Memory:2072 kb
****************************************************************/