#include <bits/stdc++.h>
using namespace std;
typedef long long lint;

lint N, p[10];
string S, cur;

int rec(int idx){
    if(idx==(cur.size()+1)/2){
        if(stoi(cur)<=N) return 1;
        return 0;
    }

    int res = 0;
    for(char i='0';i<='9';i++){
        cur[idx] = cur[cur.size()-1-idx] = i;
        res += rec(idx+1);
        cur[idx] = cur[cur.size()-1-idx] = '0';
    }
    return res;
}

int main(){
    cin >> N;

    p[0] = 1;
    for(int i=1;i<10;i++) p[i] = p[i-1] * 10;

    N = N / lint(1e9+1);
    S = to_string(N);

    for(int i=0;i<S.size();i++) cur += '0';

    lint ans = 0;
    int k = S.size();
    for(int i=1;i<k;i++) ans += 9 * p[(i-1)/2];

    for(char i='1';i<='9';i++){
        cur[0] = cur[cur.size()-1] = i;
        ans += rec(1);
        cur[0] = cur[cur.size()-1] = '0';
    }

    cout << ans << endl;
    return 0;
}