def superDigit(n, k):
    def solve(n):
        if len(n)==1:
            return n[0]
        sum = 0
        for digit in n:
            sum+=int(digit)
        return solve(list(str(sum)))
    
    sum=0
    for digit in n:
        sum+=int(digit)
    sum*=k
    
    result = solve(list(str(sum)))
    return result