#include <bits/stdc++.h>
using namespace std;
int main() {
  double r, x1, x2, x3, x4;
  scanf("%lf %lf %lf %lf %lf", &r, &x1, &x2, &x3, &x4);
  double dis = sqrt((x1 - x3) * (x1 - x3) + (x2 - x4) * (x2 - x4));
  x1 = ceil((dis) / (2 * r));
  printf("%.0lf\n", x1);
  return 0;
}
