a, b = input().split()

if len(a) != len(b):
    print(max([int(a), int(b)]))
    

else:
    for i,j in zip(list(a),list(b)):
        if i == j:
            pass
        
        elif i == '4' and j == '7':
                print(a)
                break
        elif i == '7' and j == '4':
                print(b)
                break
        else:
            if i > j:
                print(a)
                break
            else:
                print(b)
                break