#include <bits/stdc++.h>
using namespace std;
int main() {
  long long int r, x, y, xx, yy, ll;
  cin >> r >> x >> y >> xx >> yy;
  xx -= x;
  yy -= y;
  x = 0;
  y = 0;
  float l;
  l = sqrt(xx * xx + yy * yy);
  ll = l;
  if (l / (float)ll == 1 || l == 0) {
    cout << (ll / (2 * r)) << endl;
  } else {
    cout << (ll / (2 * r)) + 1 << endl;
  }
}
