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