import sys

a,b=sys.stdin.readline().split(" ")
a = a.strip()
b = b.strip()

if len(a) > len(b):
    print a
elif len(b) > len(a):
    print b
else:
    for i in range(0, len(a)):
        if a[i] == "4" and b[i] == "7":
            print a
            sys.exit(0)
        elif b[i] == "4" and a[i] == "7":
            print b
            sys.exit(0)
        else:
            if ord(b[i]) > ord(a[i]):
                print b
                sys.exit(0)
            elif ord(a[i]) > ord(b[i]):
                print a
                sys.exit(0)