N = int(input())
N //= (10 ** 9 + 1)

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