# -*- coding: utf-8 -*-
inp = raw_input().split()
A = inp[0]
B = inp[1]
N = max(len(A), len(B))
A = list(A.rjust(N, "0"))
B = list(B.rjust(N, "0"))
for i in range(0, N,):
    if int(A[i]) > int(B[i]):
        if A[i] == "7" and B[i] == "4":
            print "".join(B)
            exit()
        else:
            print "".join(A)
            exit()
    elif int(B[i]) > int(A[i]):
        if B[i] == "7" and A[i] == "4":
            print "".join(A)
            exit()
        else:
            print "".join(B)
            exit()