N = int(input())
s = N // (10**9 + 1)
ans = 0

for i in range(1, 10):
    if i <= s:
        ans += 1
        
for i in range(1, 10**5):
    if int(str(i)+str(i)[::-1]) <= s:
        ans += 1
    
    for j in range(0, 10):
        if int(str(i)+str(j)+str(i)[::-1]) <= s:
            ans += 1

print(ans)