#include <bits/stdc++.h>
using namespace std;
int main(){
	float s,a;
	cin>>a;
	if(a<=20){
		s=a*1.68;
	}
	if(a>20){
		s=a*1.98;
	}printf("%.2f",s);
}

/**************************************************************
	Problem: 1643
	User: tonghuawei
	Language: C++
	Result: Accepted
	Time:16 ms
	Memory:2072 kb
****************************************************************/