import java.util.Scanner;

public class DataCostCalculator {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        double dataUsed = sc.nextDouble();
        
        // Check constraints
        if (dataUsed <= 0 || dataUsed > 50.0) {
            System.out.println("Invalid Input");
        } else {
            if (dataUsed <= 2.0) {
                System.out.println(0); // No extra cost if within 2 GB
            } else {
                double extraGB = dataUsed - 2.0;
                int totalCost = (int) (extraGB * 20); // ₹20 per extra GB
                System.out.println(totalCost);
            }
        }
        sc.close();
    }
}