from itertools import product
N = int(input())
l = len(str(N))
s = [str(i) for i in range(10)]
res = 0
if l < 10:
    exit(print(0))
for i in range(10, l+1):
    z = 18-i
    nz = i-9
    c = 1 if nz%2==0 else 0
    cc = (nz+1)//2
    for v in product(s, repeat=cc):
        if v[0] == '0':
            continue
        vv = ''.join(v)
        V = vv+vv[::-1] if c == 1 else vv+vv[1:][::-1]
        # print(V)
        if int(V+'0'*z+V) <= N:
            # print(int(V+'0'*z+V))
            res += 1
print(res)