#include<bits/stdc++.h>
using namespace std;
#define rep(i,a,b) for(int i=a;i<b;i++)




typedef long long ll;
ll N;
//-----------------------------------------------------------------
int main() {
	cin >> N;

	int ans = 0;
	rep(i, 1, 101010) {
		string s = to_string(i);
		int n = s.length();

		// 奇数個の回文数
		ll x = 0;
		rep(i, 0, n - 1) x = x * 10 + s[i] - '0';
		x = x * 10 + s[n - 1] - '0';
		rep(i, 0, n - 1) x = x * 10 + s[n - 2 - i] - '0';

		ll a = x;
		rep(i, 0, 9) a *= 10;
		a += x;

		if (0 <= a && a <= N) ans++;

		// 偶数個の回文数
		ll xx = 0;
		rep(i, 0, n) xx = xx * 10 + s[i] - '0';
		rep(i, 0, n) xx = xx * 10 + s[n - 1 - i] - '0';
		
		ll b = xx;
		rep(i, 0, 9) b *= 10;
		b += xx;

		if (0 <= b && b <= N) ans++;
	}

	cout << ans << endl;
}