import java.util.*;

public class CreditTryAll4 {

    public static void main(String[] args) {
	int numValid = 0, numInvalid = 0;

	// try all 4-digit credit card numbers
	for (int i=0; i<10; i++) {
	    for (int j=0; j<10; j++) {
		for (int k=0; k<10; k++) {
		    for (int l=0; l<10; l++) {
			String cardNum = "";

			cardNum = cardNum + i; // here, "+" concatenates strings
			cardNum = cardNum + j;
			cardNum = cardNum + k;
			cardNum = cardNum + l;

			// see if card is valid
			if (  (luhnSum(cardNum) % 10) == 0) {
			    // yes!
			    numValid++;
			} else {
			    // no.
			    numInvalid++;
			}
		    }
		}
	    }
	}

	System.out.println("num valid: " + numValid);
	System.out.println("num invalid: " + numInvalid);

	double percentValid;

	percentValid = 100.0 * ((double) numValid) / 
	    (double) (numInvalid + numValid);
	System.out.println("percent valid: " + percentValid);
    }

    // this method accepts a credit card number as a parameter,
    // computes the sum according to the Luhn algorithm, and
    // returns that sum
    public static int luhnSum(String number) {
	int sum = 0;

	// Add up the digits formed by doubling every other digit
	for (int i=number.length()-2; i>=0; i = i-2) {
	    char c = number.charAt(i);
	    int n = 2 * Character.getNumericValue(c);
	    sum = sum + n/10 + n%10;	// Break into two digits and add
	}
	// Add the remaining digits
	for (int i=number.length()-1; i>=0; i = i-2) {
	    char c = number.charAt(i);
	    int n = Character.getNumericValue(c);
	    sum = sum + n;
	}
	return sum;
    }
}