#include <stdio.h>
using namespace std;
int main() {
    double weight;  
    double fee;     
    scanf("%lf", &weight);
    if (weight <= 20) {
        fee = weight * 1.68;
    } else {
        fee = weight * 1.98;
    }
    printf("%.2f\n", fee);  
    return 0;
}
/**************************************************************
	Problem: 1643
	User: fuhoubin
	Language: C++
	Result: Accepted
	Time:11 ms
	Memory:1144 kb
****************************************************************/