#include<bits/stdc++.h>
using namespace std;
int main(){
	int n;
	cin>>n;
	if(n>=10.0){
		printf("%.1f",2.0*n);
	}else{
		printf("%.1f",2.2*n);
	}

	return 0;
}
/**************************************************************
	Problem: 1303
	User: linyuhang
	Language: C++
	Result: Accepted
	Time:9 ms
	Memory:2072 kb
****************************************************************/