#include <bits/stdc++.h>
using namespace std;
template <class T>
inline T big(T a, T b) {
  return a > b ? a : b;
}
template <class T>
inline T small(T a, T b) {
  return a < b ? a : b;
}
int main(void) {
  long i, j;
  long r, x1, y1, x2, y2;
  long nx, ny;
  long dx, dy;
  long ans;
  long dis;
  long count = 0;
  double disis = 0;
  cin >> r >> x1 >> y1 >> x2 >> y2;
  dx = x2 - x1;
  dy = y2 - y1;
  dis = dx * dx + dy * dy;
  disis = (double)dis;
  disis = sqrt(disis);
  disis -= 0.0000000001;
  count = disis / (2 * r) + 1;
  cout << count << endl;
  return 0;
}
