import sys

def solve():
    N = int(input())
    M = N // (10**9 + 1)
    ans = 0

    k = [0, 9, 9, 90, 90, 900, 900, 9000, 9000, 90000]

    d = 1
    while 10**d <= M:
        ans += k[d]
        d += 1
    d -= 1

    e = 1
    while 10**d * e <= M:
        ans += max(1, k[max(0, d - 2)])
        e += 1
    e -= 1

    if d - 2 >= 0:
        uni = 10**d + 1
        f = 0
        while uni*e + f*10 <= M:
            fs = str(f).zfill(d - 2)
            if(fs == reversed(fs)):
                ans += 1
            f += 1

    print(ans)


def debug(x, table):
    for name, val in table.items():
        if x is val:
            print('DEBUG:{} -> {}'.format(name, val), file=sys.stderr)
            return None

if __name__ == '__main__':
    solve()