#include <bits/stdc++.h>
using namespace std;
int main() {
  int r, x, y, x1, y1;
  cin >> r >> x >> y >> x1 >> y1;
  int xx = x - x1;
  int yy = y - y1;
  double d = sqrt(xx * xx + yy * yy);
  cout << (int)(ceil(d / r / 2));
  return 0;
}
