N = input()
L = len(N)
N = int(N)
cnt = 0
for i in range(3, L+1, 3):
    keta = i//3
    for j in range(10**(keta-1), 10**keta):
        c = str(j)
        if int(c*3)<=N:
            cnt+=1
        else:
            break
print(cnt)