#include <iostream>
#include <vector>
#include <string>
#include <algorithm>
#include <cmath>

#define rep(i,n) for(i=0; i<n; ++i)
#define in(a) cin >> a
#define out(a,b) cout << a << b
using namespace std;
using lint = long long;

int main(void){
    int i, j;
    int n, m;
    int cnt = 0, ans = 0;
    lint N;
    in(N);
    
    lint ev, ll_plus;
    int pl_cnt=8, a=0;
    while(1){
        if(cnt%pl_cnt==0){
            if(ev%10==9){
                pl_cnt=10*pl_cnt+9;
                cnt=0;
            }
            ev=1*pow(10,a)+10*pow(10,2*a)+100*pow(10,3*a);
            ll_plus=1+pow(10,a+1)+pow(10,2*(a+1));
            a++;
            if(N<ev)    break;
            ans++;
        }
        ev+=ll_plus;
        cnt++;
        if(N<ev)    break;
        ans++;
    }
    
    cout << ans << endl;

    return 0;
}