#include <bits/stdc++.h>
using namespace std;
int main() {
  int r, x, y, x1, y1;
  float res = 0, d;
  cin >> r >> x >> y >> x1 >> y1;
  d = sqrt((x - x1) * (x - x1) + (y - y1) * (y - y1));
  if (d == 0)
    cout << 0;
  else if (d <= 2 * r)
    cout << 1;
  else {
    res = d - r - r;
    res = int(res / (2 * r)) + 2;
    cout << res;
  }
  return 0;
}
