a, b = input().split()
n = len(a)
m = len(b)
if n > m:
    print(a)
elif n < m:
    print(b)
else:
    for i in range(n):
        if a[i] == b[i]:
            continue
        if a[i] == '4' and b[i] == '7':
            print(a)
        elif a[i] == '7' and b[i] == '4':
            print(b)
        elif int(a[i]) > int(b[i]):
            print(a)
        elif int(a[i]) < int(b[i]):
            print(b)
        break