import math
import sys


def input(): return sys.stdin.readline().rstrip('\n')


def main():
    a, b = input().split()
    if len(a) != len(b):
        print(a if len(a) > len(b) else b)
        return
    for i, j in zip(a, b):
        if (i, j) == ('4', '7'):
            print(a)
            return
        if (i, j) == ('7', '4'):
            print(b)
            return
        if i != j:
            print(a if i > j else b)
            return
    print(a)


if __name__ == '__main__':
    main()