def A():
    print(a)
    exit()
def B():
    print(b)
    exit()

a, b = input().split()
if len(a) > len(b):
    A()
elif len(a) < len(b):
    B()

for ax, bx in zip(a, b):
    ax, bx = int(ax), int(bx)
    if ax == bx:
        continue
    if ax == 4 and bx == 7:
        A()
    elif ax == 7 and bx == 4:
        B()
    elif ax > bx:
        A()
    elif ax < bx:
        B()