#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: chenjiahui
	Language: C++
	Result: Accepted
	Time:8 ms
	Memory:2072 kb
****************************************************************/