#include <bits/stdc++.h>
using namespace std;
int main() {
  long long n;
  cin >> n;
  long long a[18] = {1,  2,  3,  4,  5,  6,  7,  8,  9,
                     19, 29, 39, 49, 59, 69, 79, 89, 99};
  if (n > 10) cout << a[19];
}
