#include<bits/stdc++.h>
using namespace std;
int main(){
	double q;
	int n;
	cin>>n;
	if(n<=10)q=n*2;
	else q=n*2*0.9;
	cout<<fixed<<setprecision(1)<<q<<endl;
	return 0;
}

/**************************************************************
	Problem: 1636
	User: admin
	Language: C++
	Result: Accepted
	Time:22 ms
	Memory:2072 kb
****************************************************************/