#include <bits/stdc++.h>
using namespace std;
int main() {
  long long int r, x1, y1, x2, y2;
  cin >> r >> x1 >> y1 >> x2 >> y2;
  double dist = sqrt(pow(x1 - x2, 2) + pow(y1 - y2, 2)) - (double)r;
  long long int count = dist / r;
  if (count < 0)
    cout << 0;
  else
    cout << count;
}
