#include <iostream>
#include <string>
#include <algorithm>
#include <iostream>
#include <string>
#include <algorithm>
#include <vector>
#include <iomanip>
#include <cmath>
#include <stdio.h>
#include <queue>
#include <deque>
#include <cstdio>
#include <set>
#include <map>
#include <bitset>
#include <stack>
#include <cctype>
using namespace std;
int main() {
	long long n;
	cin >> n;
	n /= 1000000001;
	int co = 0;
	for (int i = 1; i <= 50000; i++) {
		string s = to_string(i);
		string s1 = s;
		reverse(s1.begin(), s1.end());
		string s2 = s + s1;
		string s3 = s + s1.substr(1, s1.size() - 1);
		if (stoll(s2) <= n) {
			co++;
		}
		if (stoll(s3) <= n) {
			co++;
		}
	}
	cout << co << endl;
}