#include <bits/stdc++.h>
using namespace std;
int main() {
  long long r, x, y, x_, y_;
  cin >> r >> x >> y >> x_ >> y_;
  long double dist = sqrt((x - x_) * (x - x_) + (y - y_) * (y - y_));
  cout << ceil(dist / r / 2) << endl;
  return 0;
}
