Day 26 Biggest Digit In A Number

''' Read input from STDIN. Print your output to STDOUT '''
    #Use input() to read input from STDIN and use print to write your output to STDOUT

def main():
    n = int(input())
    maxx = 0
    while n > 0 :
        rem = n%10
        if rem > maxx:
            maxx = rem
        n /= 10
    print(maxx,end='')
    
main()