n = int(input())

ans = 0
for i in range(1,10**5):
    s = str(i)
    x = int(s + s[::-1])
    if x * 10 ** 9 + x <= n:
        ans += 1
    x = int(s + s[-2::-1])
    if x * 10 ** 9 + x <= n:
        ans += 1
print(ans)