A,B = input().split()
ka = len(A)
kb = len(B)
if ka>kb:
    print(A)
elif kb>ka:
    print(B)
else:
    for i in range(ka):
        a = int(A[i])
        b = int(B[i])
        if a==b:continue
        if a==4 and b==7:
            print(A)
            break
        elif a==7 and b==4:
            print(B)
            break
        elif a>b:
            print(A)
            break
        else:
            print(B)
            break