#include <bits/stdc++.h>
using namespace std;
int main() {
  ios_base::sync_with_stdio(false);
  int r, x, y, x2, y2;
  cin >> r >> x >> y >> x2 >> y2;
  if (x == x2 && y == y2)
    cout << 0;
  else {
    double dr = (double)r;
    double dx = (double)x;
    double dy = (double)y;
    double dx2 = (double)x2;
    double dy2 = (double)y2;
    double rast = sqrt((dx - dx2) * (dx - dx2) + (dy - dy2) * (dy - dy2));
    cout << ceil(rast / (2.0 * dr));
  }
  return 0;
}
