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