import sys
from bisect import bisect

def solve():
    n = int(input())

    n //= 10**9 + 1
    ans = 0

    palis = []

    for k in range(1, 10):
        make_palindrome2(0, k, 0, palis)

    ans = bisect(palis, n) - 1

    print(ans)

def make_palindrome2(i, n, pal, palis):
    if 2*i == n:
        palis.append(pal)
        return
    elif 2*i == n - 1:
        for d in range(10):
            palis.append(pal + d * 10**i)
        return
    elif i == 0:
        for d in range(1, 10):
            make_palindrome2(i + 1, n, pal + d * (10**(n - 1) + 1), palis)
    else:
        for d in range(10):
            make_palindrome2(i + 1, n, pal + d * (10**(n - 1 - i) + 10**i), palis)

def make_palindrome(i, n, s, a):
    if i == n:
        a.append(int(s))
        return
    elif n - i == 2:
        for j in range(1, 10):
            make_palindrome(i + 2, n, str(j) + s + str(j), a)
    else:
        for j in range(0, 10):
            make_palindrome(i + 2, n, str(j) + s + str(j), a)

if __name__ == '__main__':
    solve()