#include<iostream>
#include<algorithm>
using namespace std;
typedef long long ll;

const ll x = 1e9 + 1;

int main(){
    ll n;
    cin >> n;

    int ans = 0;
    ll up = 1;
    while(up*up < n/x) up *= 10;

    ll tmp = 0;
    for(int i = 0; i < 9; i++){
        tmp += x;
        if(tmp <= n)    ans++;
    }
    
    for(ll i = 1; i <= up; i++){
        string s = to_string(i);
        string t = s;
        reverse(t.begin(), t.end());
        s += t;
        ll j = stoll(s);
        if(j <= n/x)    ans++;
    }

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