#include<bits/stdc++.h>
using namespace std;
int main(){
	float n;
	cin>>n;
	if(n>10){
		cout<<fixed<<setprecision(1)<<n*2*0.9;
	} else{
		cout<<fixed<<setprecision(1)<<n*2;	
	}
	return 0;
}
/**************************************************************
	Problem: 1636
	User: linmiaoling
	Language: C++
	Result: Accepted
	Time:18 ms
	Memory:2072 kb
****************************************************************/