#include <bits/stdc++.h>
using namespace std;
int main() {
  int r, x, y, x1, y1;
  cin >> r >> x >> y >> x1 >> y1;
  double s;
  s = sqrt((x - x1) * (x - x1) + (y - y1) * (y - y1));
  if ((int)s % (2 * r) == 0) {
    cout << s / (2 * r) << endl;
  } else {
    cout << s / (2 * r) + 1 << endl;
  }
  return 0;
}
