# coding:utf-8

A, B = input().split()
A1 = list(A)
B1 = list(B)
a = [0]*14
b = [0]*14
for i in range(len(A1)):
    a[13-i]=int(A1[-1-i])
for i in range(len(B1)):
    b[13-i]=int(B1[-1-i])
for i in range(14):
    if a[i]==b[i]:
        continue
    elif a[i]==4 and b[i]==7:
        print(A)
        break
    elif a[i]==7 and b[i]==4:
        print(B)
        break
    elif a[i]>b[i]:
        print(A)
        break
    elif a[i]<b[i]:
        print(B)
        break