#include <bits/stdc++.h>

#define show(x) cerr << #x << " = " << x << endl

using namespace std;
using ll = long long;
using pii = pair<int, int>;
using vi = vector<int>;

template <typename T>
ostream& operator<<(ostream& os, const vector<T>& v)
{
    os << "sz=" << v.size() << "\n[";
    for (const auto& p : v) {
        os << p << ",";
    }
    os << "]\n";
    return os;
}

template <typename S, typename T>
ostream& operator<<(ostream& os, const pair<S, T>& p)
{
    os << "(" << p.first << "," << p.second
       << ")";
    return os;
}


constexpr ll MOD = 1e9 + 7;

template <typename T>
constexpr T INF = numeric_limits<T>::max() / 100;

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

    ll n;
    cin >> n;
    constexpr ll mod = (ll)1e9 + 1LL;
    const ll num = n / mod;
    constexpr ll max = 9999;
    ll cnt = min(num, 9LL);

    for (ll i = 1; i <= max; i++) {
        string s = to_string(i);
        string rev = s;
        reverse(rev.begin(), rev.end());
        for (ll d = -1; d < 10; d++) {
            const string sep = (d == -1) ? "" : to_string(d);
            const ll v = stoll(s + sep + rev);
            if (0 < v and v <= num) {
                cnt++;
            }
        }
    }
    cout << cnt << endl;

    return 0;
}