import math
import sys
def S(): return sys.stdin.readline().rstrip()
def I(): return int(sys.stdin.readline().rstrip())
def MI(): return map(int, sys.stdin.readline().rstrip().split())
def LI(): return list(map(int, sys.stdin.readline().rstrip().split()))
def LS(): return list(sys.stdin.readline().rstrip().split())

a, b = S().split()

if len(a) > len(b):
    print(a)
elif len(a) < len(b):
    print(b)
else:
    for i in range(len(a)):
        if a[i] == b[i]:
            continue
        else:
            if a[i] == "7" and b[i] == "4":
                print(b)
            elif a[i] == "4" and b[i] == "7":
                print(a)
            elif a[i] > b[i]:
                print(a)
            else:
                print(b)
            break