#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: wangyiyang
	Language: C++
	Result: Accepted
	Time:6 ms
	Memory:2072 kb
****************************************************************/