import bisect
n = []
for i in range(10, 19, 2):
    nn = (i-8)//2
    for j in range(1,10):
        num = int(str(j)*nn+'0'*8+str(j)*nn)
        s = 1
        while 1:
            ss = num*s
            if ss <= 10**18:
                n.append(ss)
            else:
                break
            s *= 10
            s += 1
n.sort()
N = int(input())
print(bisect.bisect_left(n, N+1))