def kaibun(y):
	x = len(str(y))
	X = [9,9]
	i = 2
	while x > i:
		if i % 2 == 0:
			X.append(X[i - 1] * 10)
		else:
			X.append(X[i - 1])
		i = i + 1
	a = sum(X[:x - 1])
	for j in range(1, x // 2 + 1):
		if j == 1:
			a = a + (int(str(y)[j - 1]) - 1) * X[x - 2 * j + 1]//9
		else:
			a = a + (int(str(y)[j - 1])) * X[x - 2 * j + 1] // 9
	if str(y)[:x//2][::-1] and str(y)[x//2 + 1:] and int(str(y)[:x//2][::-1]) < int(str(y)[x//2:]) and x % 2 == 0:
		a = a + 1 
	elif x % 2 == 1:
		a = a + int(str(y)[x//2])
		if str(y)[:x//2][::-1] and str(y)[x//2 + 1:] and int(str(y)[:x//2][::-1]) < int(str(y)[x//2 + 1:]):
			a = a + 1
	if x == 1:
		return y
	return a
n = input()
if len(n) < 10:
	print(0)
else:
	n = n[:-9]
	k = int(n)
	answer = kaibun(k)
	if len(n) == 10 and int(n)%10**9 < int(n[0]):
		answer = answer - 1
	print(answer)