#include <bits/stdc++.h>
using namespace std;
const long double eps = 1e-9;
int main() {
  long double r, x, y, x_, y_;
  cin >> r >> x >> y >> x_ >> y_;
  long double d = (double(((x - x_) * (x - x_)))) +
                  (double(((y - y_) * (y - y_)))),
              D = (double(((2.0 * (r + .0)) * (2.0 * (r + .0)))));
  int ans = floor(d / D);
  int q = 0;
  if (d / D - ans > eps) q++;
  cout << int(floor(sqrt(ans))) + q;
  return 0;
}
