#include <bits/stdc++.h>
using namespace std;
struct oxy {
  int x, y;
};
int r;
double _kc(oxy a, oxy b) {
  return sqrt((a.x - b.x) * (a.x - b.x) + (a.y - b.y) * (a.y - b.y));
}
void _solve() { int i, j; }
bool _input() {
  int i, j;
  oxy c, d;
  double kc;
  scanf("%d %d %d %d %d", &r, &c.x, &c.y, &d.x, &d.y);
  kc = _kc(c, d);
  if (kc <= r) {
    printf("0\n");
    return 1;
  }
  kc = (int)kc / r - 1;
  printf("%d\n", (int)kc);
}
int main() {
  int itest, ntest = 1;
  for (itest = 1; itest <= ntest; itest++) {
    _input();
    _solve();
  }
  return 0;
}
