#include <bits/stdc++.h>
using namespace std;
int main() {
  int r, xs, ys, xt, yt;
  while (cin >> r >> xs >> ys >> xt >> yt) {
    double distt =
        sqrt(1.0 * (yt - ys) * (yt - ys) + 1.0 * (xt - xs) * (xt - xs));
    int result = (int)distt / (2 * r);
    if (result * 2.0 * r < distt - 1e-9) result++;
    cout << result << endl;
  }
}
