a = input()
b = input()
x = [0] * 10
y = [0] * 10
for i in range(10):
    x[i] = a.count(str(i))
    y[i] = b.count(str(i))
for i in range(9, -1, -1):
    print(str(i) * min(x[i], y[i]), end='')