from itertools import count

N = 1000000001
n = int(input())
ans = 0
for i in map(str, count(1)):
    x = int(i + i[::-1])
    y = int(i + i[:-1][::-1])
    if N * x <= n:
        ans += 1
    if N * y <= n:
        ans += 1
    else:
        break

print(ans)