#include<bits/stdc++.h>
using namespace std;
int main(){
    float g,m;
    cin>>g;
    if(g<=20){
        m=1.68*g;
        printf("%.2f",m);
    }else{
        m=1.98*g;
        printf("%.2f",m);
    }
}
/**************************************************************
	Problem: 1643
	User: yangjunwen
	Language: C++
	Result: Accepted
	Time:11 ms
	Memory:2072 kb
****************************************************************/