#include <bits/stdc++.h>
using namespace std;
int main() {
  double r, x1, y1, x2, y2;
  cin >> r >> x1 >> y1 >> x2 >> y2;
  double dis = sqrt((x2 - x1) * (x2 - x1) + (y2 - y1) * (y2 - y1));
  int answer = dis / (2 * r);
  if (dis != answer * 2 * r) answer++;
  cout << answer;
  return 0;
}
