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