#include <bits/stdc++.h>
using namespace std;
int main() {
  float r, x, y, x1, y1, s;
  int t;
  cin >> r >> x >> y >> x1 >> y1;
  s = sqrt(pow(x1 - x, 2) + pow(y1 - y, 2));
  s /= (2 * r);
  t = (int)s;
  if (fabs(s - t) > 0.0000000001) t++;
  cout << t << endl;
  return 0;
}
