from fractions import gcd
from heapq import*
import math
from collections import defaultdict, Counter
import sys
sys.setrecursionlimit(10 ** 7)
MOD = 10 ** 9 + 7


def main():
    a, b = map(int, input().split())
    sa,sb = str(a),str(b)
    if len(sa) > len(sb):
        print(a)
    elif len(sa) < len(sb):
        print(b)
    else:
        for i in range(len(sa)):
            if (sa[i] == "4" and sb[i] == "7"):
                print(a)
                exit()
            elif (sa[i] == "7" and sb[i] == "4"):
                print(b)
                exit()
            elif int(sa[i]) > int(sb[i]):
                print(a)
                exit()
            elif int(sa[i]) < int(sb[i]):
                print(b)
                exit()



if __name__ == '__main__':
    main()