include<bits/stdc++.h>

using namespace std; const int N = 10; int n, a[N], p; int main() { cin >> n; p = 1; int m = 0; while (p < n) { m = m + 1; a[m] = 9 * p * m; p = p * 10; int page = 0; for(int i = 1, i <= m, i++) if (n > a[I]) { page += a[I]/i; n = n - a[I]; } else{ if (n % i == 0) page = 0; else page += n/i;

      break;

      }
}

cout << page;
}