from itertools import count

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

print(ans)