/**
 *   @FileName	a.cpp
 *   @Author	kanpurin
 *   @Created	2020.06.05 00:38:56
**/

#include "bits/stdc++.h" 
using namespace std; 
typedef long long ll;

string next_str(string s) {
    int l = 0, r = s.size() - 1;
    while (r - l > 1) {
        l++;
        r--;
    }
    if (s[l] != '9') {
        s[l]++;
        if (l != r) {
            s[r]++;
        }
        return s;
    }
    while (s[l] == '9') {
        s[l] = '0';
        s[r] = '0';
        l--;
        r++;
    }
    if (l == -1) {
        s[0] = '1';
        s.push_back('1');
        return s;
    }
    s[l]++;
    s[r]++;
    return s;
}
int to_num(string s){
    int res = 0;
    for (int i = 0; i < s.size(); i++) {
        res*=10;
        res += s[i]-'0';
    }
    return res;
}
int main() {
    ll n;
    cin >> n;
    const int mod = 1e9 + 1;
    ll m = n / mod;
    
    string t = "1";
    int ans = 0;
    while(to_num(t) <= m) {
        ans++;
        
        t = next_str(t);
    }
    cout << ans << endl;
    return 0;
}