#include <bits/stdc++.h>
using namespace std;
int main() {
  long long int i, j, k, l, m, n, d1, d2, x1, x2, y1, y2, r;
  double d = 0;
  cin >> r >> x1 >> y1 >> x2 >> y2;
  d1 = pow((x2 - x1), 2);
  d2 = pow((y2 - y1), 2);
  d = sqrt(d1 + d2);
  m = d;
  if (d == m) {
    cout << d / (2 * r) << endl;
  } else {
    m++;
    while (m % (2 * r) != 0) {
      m++;
    }
    cout << m / (2 * r) << endl;
  }
  return 0;
}
