def is_num(n):
com = n * n - n
j = 0
a=1
sum =0
while j < len(str(n)):
a = a * 10
j = j + 1
if com % a == 0:
sum = 1
return sum

if name =='main':
while True:
try:
n = input()
sum = 0
a=1

        for i in range(n):
            if is_num(i):
                sum = sum+1

        print sum
    except:
        break