a,b = input().split()
if len(a) < len(b):
    print(b)
elif len(a) > len(b):
    print(a)
else:
    for i,j in zip(a,b):
        if i != j: break
    if i not in "47" or j not in "47":
        if int(i) < int(j):
            print(b)
        else:
            print(a)
    else:
        if int(i) < int(j):
            print(a)
        else:
            print(b)