#include <bits/stdc++.h>
using namespace std;
int main() {
  int r, x, y, x1, y1, res = 0;
  float dist;
  scanf("%d %d %d %d %d", &r, &x, &y, &x1, &y1);
  dist = sqrt((y1 - y) * (y1 - y) + (x1 - x) * (x1 - x));
  res = ((int)ceil((dist / r / 2)));
  printf("%d", res);
  return 0;
}
