#include <iostream>
#include <iomanip>
#include <cmath>
using namespace std;
int main(){
	double g;
	cin>>g;
	double money=0;
	if(g>20){
		money=g*1.98;
	}
	else{
		money=g*1.68;
	}
	cout<<fixed<<setprecision(2)<<money;
	return 0;
}