#include "bits/stdc++.h"
using namespace std;
#define FOR(i,j,k) for(int (i)=(j);(i)<(int)(k);++(i))
#define rep(i,j) FOR(i,0,j)
#define each(x,y) for(auto &(x):(y))
#define mp make_pair
#define mt make_tuple
#define all(x) (x).begin(),(x).end()
#define debug(x) cout<<#x<<": "<<(x)<<endl
#define smax(x,y) (x)=max((x),(y))
#define smin(x,y) (x)=min((x),(y))
#define MEM(x,y) memset((x),(y),sizeof (x))
#define sz(x) (int)(x).size()
#define pb push_back
typedef long long ll;
typedef pair<int, int> pii;
typedef vector<int> vi;
typedef vector<ll> vll;

const int M = 1000000001;
ll N;

int main(){
    ios::sync_with_stdio(false);
    cin.tie(0);

    cin >> N;
    ll m = N / M;
    // m以下の整数のうち回文となるもの

    ll ans = 0;

    // 偶数長
    for(ll i = 1; ; ++i) {
        string s = to_string(i), t = s;
        reverse(all(t));
        ll x = stoll(s + t);
        if(x > m)break;
        ans++;
    }

    // 奇数長
    for(ll i = 0; i <= 9; ++i) {
        if(i!=0 && i <= m)++ans;

        for(ll j = 1;; ++j) {
            string s = to_string(j), t = s;
            reverse(all(t));
            ll x = stoll(s + to_string(i) + t);
            if(x > m)break;
            ans++;
        }
    }


    cout << ans << endl;
}