public static int superDigit(string n, int k)
    {
        do
        {
            long sum = 0;
            foreach(char c in n)
            {
                sum += int.Parse(c.ToString());
            }
            sum *= k;
            k=1;
            n = sum.ToString();
        }while(n.Count()!=1);
        
        return int.Parse(n);
    }

function superDigit(n: string, k: number): number {
  let sum = 0;

  for (let char of n) {
    sum += Number(char);
  }

  sum *= k;

  if (sum <= 9) return sum;

  return superDigit(String(sum), 1);
}

function superDigit($n, $k) {
    $x = array_sum(str_split($n)) * $k;

    while ($x >= 10) {
        $x = array_sum(str_split($x));
    }

    return $x;
}

 public static int superDigit(String n, int k) {
        long sum = 0;
        for (char digit : n.toCharArray()) {
            sum += Character.getNumericValue(digit);
        }

        sum *= k;
        return superDigitHelper(sum);
    }

    private static int superDigitHelper(long n) {
        if (n < 10) return (int) n;

        long nextSum = 0;
        while (n > 0) {
            nextSum += n % 10;
            n /= 10;
        }

        return superDigitHelper(nextSum);
    }

def superDigit(n, k):
    # Write your code here
    res = sum(int(i) for i in str(n)) * k
    while res > 10:
        res = sum(int(i) for i in str(res))
    return res