#include <bits/stdc++.h>
using namespace std;
int main() {
  long long int r, x, y, a, b, q, w;
  cin >> r >> x >> y >> a >> b;
  q = (x - a) * (x - a);
  q = sqrt(q);
  w = (y - b) * (y - b);
  w = sqrt(w);
  q = (q + w) / 2;
  cout << q / r;
}
