#include <bits/stdc++.h>
using namespace std;
const int MOD = 1000000007;
void solve() {
  int r, x1, x2, y1, y2;
  cin >> r >> x1 >> y1 >> x2 >> y2;
  double d = sqrt((x2 - x1) * (x2 - x1) + (y2 - y1) * (y2 - y1));
  cout << 1LL * ceil((d / (2 * r)));
}
int main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);
  cout.tie(0);
  ;
  solve();
  return 0;
}
