#include<bits/stdc++.h> 
using namespace std;
int main()
{
	int n;
	double a,b,c;
	cin>>n;
	a=n*0.8;
	b=n*0.9;
	c=(a+b+n)/3;
	cout<<c<<endl;
	return 0;
}
/**************************************************************
	Problem: 1613
	User: zhangchenyu
	Language: C++
	Result: Accepted
	Time:9 ms
	Memory:2072 kb
****************************************************************/