#include <bits/stdc++.h>
#define FOR(i,bg,ed) for(ll i=(bg);i<(ed);i++)
#define REP(i,n) FOR(i,0,n)
#define MOD 1000000007
#define int long long
using namespace std;
typedef long long ll;
const int INF = 1e9;



signed main()
{
    ll N, M, cnt = 0;

    cin >> N;
    M = N / 1000000001;
    for (int i=1; i<100000; i++) {
        string V = to_string(i);
        string S = V, T = V;
        reverse(V.begin(), V.end());
        S += V; T += V.substr(1, V.size()-1);
        if (stoll(S) <= M) cnt++;
        if (stoll(T) <= M) cnt++;
    }
    cout << cnt << endl;
}