#include<bits/stdc++.h>
using namespace std;
int main(){
    float a;
    cin>>a;
    if(a>10){
        printf("%.1f",a*2*0.9);
    }else{
        printf("%.1f",a*2);
    }
     
     
} 
/**************************************************************
	Problem: 1636
	User: yangjunwen
	Language: C++
	Result: Accepted
	Time:11 ms
	Memory:2072 kb
****************************************************************/