#include<bits/stdc++.h> 
using namespace std;
int main(){
    int n1;
    float n2,n3,j;
    cin>>n1;
    n2=n1*0.9;
    n3=n1*0.8;
    j=(n1+n2+n3)/3.0;
    printf("%.1f",j);
	 
} 
/**************************************************************
	Problem: 1613
	User: yangjunwen
	Language: C++
	Result: Accepted
	Time:7 ms
	Memory:2072 kb
****************************************************************/