#include <bits/stdc++.h>

using namespace std;

int main()
{
    freopen("mk.inp", "r", stdin);
    freopen("mk.out", "w", stdout);
    int n, sum = 0;
    cin >> n;
    for (int i = 1; i <= n; i++) {
        int x = i;
        while (x) {
            sum += x % 10;
            x /= 10;
        }
    }
    cout << sum;
    return 0;
}

#include <bits/stdc++.h>
#define ll long long
using namespace std;
#define MOD 1000000007
#define nmax 10000005
ll tcs (string s)
{
    ll cnt = 0;
    for (char c: s) cnt += c - '0';
    return cnt;
}
ll n;
string r;
int main() {
    cin >> n;
    for (ll i = 1; i <= n; ++i)
    {
        r += to_string(i);
    }
    cout << tcs(r);
    return 0;
}