#include <bits/stdc++.h>
using namespace std;
int main() {
  double r, x, y, X, Y;
  scanf("%lf%lf%lf%lf%lf", &r, &x, &y, &X, &Y);
  printf("%d\n", (int)ceil(hypot(x - X, y - Y) / 2 / r));
  return 0;
}
