#include <bits/stdc++.h>
using namespace std;
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  double r, x1, y1, x2, y2;
  cin >> r >> x1 >> y1 >> x2 >> y2;
  int ans = 0;
  ans = ceil(sqrt((x2 - x1) * (x2 - x1) + (y2 - y1) * (y2 - y1)) / (2 * r));
  cout << ans;
  return 0;
}
