#include <bits/stdc++.h>
using namespace std;
const int N = 500 + 5;
const int INF = 2e9 + 5;
const int mod = 1e9 + 7;
int a[N][N], b[N];
int main() {
  double r, x1, y1, x2, y2;
  cin >> r >> x1 >> y1 >> x2 >> y2;
  cout << ceil(sqrt((x2 - x1) * (x2 - x1) + (y1 - y2) * (y1 - y2)) / (2 * r))
       << endl;
  return 0;
}
