#O(logN)

n = input()
if len(n) % 3:
    ans = int(('9' * ((len(n)) // 3)) if len(n) >= 3 else '0')

else:
    k = len(n) // 3
    n1 = int(n[:k])
    n2 = int(n[k:2 * k])
    n3 = int(n[2 * k:])

    if n1 <= n2 and n1 <= n3:
        ans = n1
    else:
        ans = n1 - 1
print(ans)