A, B = map(str, input().split())

if len(A) > len(B):
    print(A)
elif len(A) < len(B):
    print(B)
else:
    for a, b in zip(A, B):
        if a == '4' and b == '7':
            print(A)
            exit()
        elif a == '7' and b == '4':
            print(B)
            exit()
        elif  int(a) > int(b):
            print(A)
            exit()
        elif int(a) < int(b):
            print(B)
            exit()