#include <stdio.h>

using namespace std;

int main()
{
    int amount;
    double ans = 20;
    scanf("%d", &amount);
    if(amount <= 0) {
        printf("You have entered an invalid amount! - please enter a valid number");
        return 0;
    } else if (amount > 50) {
        printf("book limit was exceeded");
        return 0;
    } else if (0 <= amount && amount <= 9) {
        ans -= ans*5/100;
    } else if (10 <= amount && amount <= 14) {
        ans -= ans*10/100;
    } else if (15 <= amount && amount <= 19) {
        ans -= ans*15/100;
    } else if (20 <= amount && amount <= 49) {
        ans -= ans*20/100;
    }

    ans *= amount;

    printf("%f", ans);

    return 0;
}