#include <bits/stdc++.h>
using namespace std;
const int T = 1e5 + 100;
int main() {
  double n, a, b, c, d;
  cin >> n >> a >> b >> c >> d;
  double a1 = 0, a2 = 0, t = 0;
  a1 = sqrt((a - c) * (a - c) + (b - d) * (b - d));
  a1 /= 2.0 * n;
  t = a1;
  if (a1 - t > 0) t++;
  cout << t;
  return 0;
}
