a,b=input().split()
if len(a)>len(b):
    print(a)
elif len(b)>len(a):
    print(b)
else:
    for i in range(len(a)):
        x=a[i]
        y=b[i]
        if x=="4" and y=="7":
            print(a)
            exit()
        if x=="7" and y=="4":
            print(b)
            exit()
        if x>y:
            print(a)
        if y>x:
            print(b)