#include <bits/stdc++.h>
using namespace std;
int main() {
  long long int r, x, y, x1, y1;
  cin >> r >> x >> y >> x1 >> y1;
  int d;
  double rc;
  rc = sqrt((x - x1) * (x - x1) + (y - y1) * (y - y1)) / (2 * r);
  d = (int)rc;
  if (rc > 0) {
    if (rc > d) d++;
  }
  cout << d;
  return 0;
}
