#include <bits/stdc++.h>
using namespace std;
int main() {
  double r, x1, y1, x2, y2;
  while (scanf("%lf%lf%lf%lf%lf", &r, &x1, &y1, &x2, &y2) != EOF) {
    double d = sqrt((x2 - x1) * (x2 - x1) + (y2 - y1) * (y2 - y1));
    if (d <= r)
      printf("0\n");
    else {
      int dd = int((d - r));
      int rr = int(r);
      int count;
      if (dd % rr == 0)
        count = dd / rr;
      else
        count = dd / rr + 1;
      printf("%d\n", count);
    }
  }
  return 0;
}
