N=input()
if len(N) < 3:
    print(0)
    exit()
if len(N)%3 != 0:
    print('9'*(len(N)//3))
    exit()
    
n=N[:len(N)//3]

for i in range(1,10**5 + 1):
    if i > int(n):
        break
    if int(str(i)*3) <= int(N):
        ans = i
print(ans)