#include<bits/stdc++.h>
using namespace std;
using ll = long long;

#define FOR(i,a,b) for(ll i=(a);i<(b);++i)
#define ALL(v) (v).begin(), (v).end()
#define p(s) cout<<(s)<<endl
#define p2(s, t) cout << (s) << " " << (t) << endl
#define br() p("")
#define pn(s) cout << (#s) << " " << (s) << endl
#define p_yes() p("Yes")
#define p_no() p("No")

const ll mod = 1e9 + 7;
const ll inf = 1e18;

template < typename T >
void vprint(T &V){
	for(auto v : V){
    	cout << v << " ";
	}
	cout << endl;
}

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

    // input
    ll N;
    cin >> N;

    ll a = N / (1e9+1);
    
    ll count = 0;

    // 偶数長さの回文
    FOR(i, 1, 10000){
        string s = to_string(i);
        reverse(ALL(s));
        stringstream ss;
        ss << i << s;
        ll v = stoi(ss.str());
        if(v<=a) count++;
    }

    // 1桁
    FOR(i, 1, 10){
        if(i<=a) count++;
    }

    // 奇数長さ(3, 5, 7)の回文
    FOR(i, 1, 1000){
        FOR(j, 0, 10){ // center
            string s = to_string(i);
            reverse(ALL(s));
            stringstream ss;
            ss << i << j << s;
            ll v = stoi(ss.str());
            if(v<=a) count++;
        }
    }

    p(count);
    
    return 0;
}