#include <cs50.h>
#include <stdio.h>

int main(void)
{
    // Get the number
    long long int number = get_long_long("Number:");
    // Determine it's length
    long long int a = number;
    int counter = 0;
    while (a > 0)
    {
        a /= 10;
        counter++;
    }
    // Turn it into an array
    int arr[counter], c = counter - 1;
    while (c >= 0)
    {
        arr[c] = number % 10;
        number /= 10;
        c--;
    }
    // Check if it's a valid credit card number
    int sum = 0;
    for (int i = counter - 2; i >= 0; i -= 2)
    {
        if (arr[i] * 2 / 10.0 > 1)
        {
            printf("%i\n", arr[i] * 2 / 10);
            printf("%i\n", arr[i] * 2 % 10);
            sum += arr[i] * 2 / 10;
            sum += arr[i] * 2 % 10;
        }
        else
        {
            sum += arr[i] * 2;
        }
    }
    for (int j = counter - 1; j >= 0; j -= 2)
    {
        sum += arr[j];
    }
    printf("%i\n", sum);
    if (sum % 10 != 0)
    {
        printf("INVALID\n");
    }
    // Determine it's type
    else
    {
       if (arr[0] == 3 && (arr[1] == 4 || arr[1] == 7))
        {
            printf("AMEX\n");
        }
        else if (arr[0] == 5 && (arr[1] == 1 || arr[1] == 2 || arr[1] == 3 || arr[1] == 4 || arr[1] == 5))
        {
            printf("MASTERCARD\n");
        }
        else
        {
        printf("VISA\n");
        }
    }
}