/* -*- coding: utf-8 -*-
 *
 * 756.cc:  No.756 チャンパーノウン定数 (1) - yukicoder
 */

#include<cstdio>
#include<cstdlib>
#include<cstring>
#include<cmath>
#include<iostream>
#include<string>
#include<vector>
#include<map>
#include<set>
#include<stack>
#include<list>
#include<queue>
#include<deque>
#include<algorithm>
#include<numeric>
#include<utility>
#include<complex>
#include<functional>
 
using namespace std;

/* constant */

/* typedef */

/* global variables */

/* subroutines */

/* main */

int main() {
  int d;
  scanf("%d", &d);

  if (d < 10) printf("%d\n", d);
  else {
    d -= 10;
    int n = d / 2 + 10;
    printf("%d\n", (d & 1) ? n % 10 : n / 10);
  }
  return 0;
}