#include <bits/stdc++.h>
using namespace std;
int main() {
  int r;
  double x1, x2, y1, y2;
  cin >> r >> x1 >> y1 >> x2 >> y2;
  double dis = pow((y2 - y1), 2.0) + pow((x2 - x1), 2.0);
  dis = sqrt(dis);
  if (dis / (2 * r) != int(dis) / (2 * r)) {
    cout << (int(dis) / (2 * r)) + 1 << endl;
  } else
    cout << (int(dis) / (2 * r)) << endl;
  return 0;
}
