a,b= map(int, input().split())
s,t = map(str, (a, b))

if len(s)!=len(t):
    if(len(s)>len(t)):
        print(a)
    else:
        print(b)
else:
    u = ('4', '7')
    ans = a
    for i in range(len(s)):
        if s[i] != t[i]:
            if s[i] in u and t[i] in u:
                if t[i] == '4':
                    ans = b
            elif t[i] > s[i]:
                ans = b
            break

    print(ans)