A, B = input().split()

if len(A) > len(B):
    print(A)
    exit()
elif len(A) < len(B):
    print(B)
    exit()

for a, b in zip(A, B):
    if a in "47" and b in "47":
        if int(a) > int(b):
            print(B)
            break
        elif int(a) < int(b):
            print(A)
            break
    else:
        if int(a) > int(b):
            print(A)
            break
        elif int(a) < int(b):
            print(B)
            break