#include<bits/stdc++.h>
using namespace std;
int main(){
    int x;
    float c;
    cin>>x;
    c=x*0.9+x*0.8+x;
    cout<<c/3.0;
    
    
	
	
}
/**************************************************************
	Problem: 1613
	User: lvrenxiang
	Language: C++
	Result: Accepted
	Time:8 ms
	Memory:2072 kb
****************************************************************/