#!/usr/bin/env pypy3

M = 10 ** 9 + 1


def is_palin(n):
    s = str(n)
    return s == s[::-1]


def count_palins_lt_p10(k):
    if k % 2 == 0:
        return 2 * (10 ** (k // 2) - 1)
    else:
        return 11 * 10 ** ((k - 1) // 2) - 2


def floor_log_10(n):
    k = len(str(n))
    return k - 1


def count_palins_le(last):
    k = floor_log_10(last)
    res1 = count_palins_lt_p10(k)
    res2 = sum(is_palin(i) for i in range(10 ** k, last + 1))
    return res1 + res2


def solve(n):
    last = n // M
    return count_palins_le(last)


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


if __name__ == '__main__':
    main()