from itertools import count

n = int(input())
ans = 0
for i in map(str, range(1, 10)):
    a = int(i + i[::-1])
    b = int(i)
    if a * 1000000001 <= n:
        ans += 1
    if b * 1000000001 <= n:
        ans += 1
    else:
        break

for i in map(str, count(10)):
    a = int(i + i[::-1])
    b = int(i + i[: (len(i) + 1) // 2][::-1])
    if a * 1000000001 <= n:
        ans += 1
    if b * 1000000001 <= n:
        ans += 1
    else:
        break

print(ans)