#include <bits/stdc++.h>
using namespace std;
int main() {
  int a, b, c, d, e, n;
  cin >> a >> b >> c >> d >> e;
  n = 0;
  double h;
  h = sqrt((b - d) * (b - d) + (c - e) * (c - e));
  if (h == 0) {
    n = 0;
  }
  if (a == 0) {
    n = 0;
  }
  if (h <= 2 * a && h > 0) {
    n = 1;
  }
  if (h > 2 * a) {
    int k;
    k = int((h - a) / 2 + 1);
    n = k + 1;
  }
  cout << n;
  return 0;
}
