import sys

def input(): return sys.stdin.readline().strip()
def list2d(a, b, c): return [[c] * b for i in range(a)]
def list3d(a, b, c, d): return [[[d] * c for j in range(b)] for i in range(a)]
def list4d(a, b, c, d, e): return [[[[e] * d for j in range(c)] for j in range(b)] for i in range(a)]
def ceil(x, y=1): return int(-(-x // y))
def INT(): return int(input())
def MAP(): return map(int, input().split())
def LIST(N=None): return list(MAP()) if N is None else [INT() for i in range(N)]
def Yes(): print('Yes')
def No(): print('No')
def YES(): print('YES')
def NO(): print('NO')
sys.setrecursionlimit(10 ** 9)
INF = 10 ** 19
MOD = 10 ** 9 + 7
EPS = 10 ** -10

S, T = input().split()

if len(S) > len(T):
    print(S)
elif len(S) < len(T):
    print(T)
else:
    N = len(S)
    for i in range(N):
        if S[i] != T[i]:
            if S[i] == '4' and T[i] == '7':
                print(S)
            elif S[i] == '7' and T[i] == '4':
                print(T)
            elif S[i] > T[i]:
                print(S)
            else:
                print(T)
            break