#include <bits/stdc++.h>
using namespace std;
struct point {
  int x, y;
};
istream &operator>>(istream &in, point &p) {
  in >> p.x >> p.y;
  return in;
}
ostream &operator<<(ostream &out, point &p) {
  out << p.x << " " << p.y;
  return out;
}
double len(struct point a, struct point b) {
  return sqrt((a.x - b.x) * (a.x - b.x) + (a.y - b.y) * (a.y - b.y));
}
int main() {
  ios_base::sync_with_stdio(NULL);
  cin.tie(NULL);
  cout.tie(NULL);
  int r;
  point a, b;
  cin >> r;
  cin >> a >> b;
  cout << ceil(len(a, b) / (r * 2));
  return 0;
}
