#include <bits/stdc++.h>
using namespace std;
int main() {
  int r, x, y, x1, y1;
  cin >> r >> x >> y >> x1 >> y1;
  double d = sqrt(pow(x - x1, 2) + pow(y - y1, 2));
  double ans = d / 2 * r;
  int ans1 = ans;
  if (ans1 == ans)
    cout << ans;
  else
    cout << ans1 + 1;
}
