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