A, B = 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)
            break

        elif (a == '7') and (b == '4'):
            print(B)
            break

        elif int(a) > int(b):
            print(A)
            break

        elif int(a) < int(b):
            print(B)
            break