#include <iostream>
#include <vector>
#include <algorithm>
#include <cmath>
#include <queue>
#include <string>
#include <map>
#include <set>
#include <stack>
#include <tuple>
#include <deque>
#include <array>
#include <numeric>
#include <bitset>
#include <iomanip>
#include <cassert>
#include <chrono>
#include <random>
#include <limits>
#include <iterator>
#include <functional>
#include <sstream>
#include <fstream>
#include <complex>
#include <cstring>
#include <unordered_map>
using namespace std;

using ll = long long;
using P = pair<int, int>;
constexpr int INF = 1001001001;
constexpr int mod = 1000000007;
// constexpr int mod = 998244353;

template<class T>
inline bool chmax(T& x, T y){
    if(x < y){
        x = y;
        return true;
    }
    return false;
}
template<class T>
inline bool chmin(T& x, T y){
    if(x > y){
        x = y;
        return true;
    }
    return false;
}

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

    ll N;
    cin >> N;
    constexpr ll NUM = 1000000001LL;

    ll ans = 0, num = 1;
    for(ll i = 1000000000LL; i <= min((ll)1e+18 - 1, N); i *= 10){
        if(N / i >= 10) ans += 9;
        else{
            for(int j = num; j <= num * 9; j += num){
                if(1000000000LL * j + j <= N)    ans += 1;
            }
        }
        num = num * 10 + 1;
    }
    
    cout << ans << endl;

    return 0;
}