#include <bits/stdc++.h>
using namespace std;
int main() {
  int x, y, x1, y1, r;
  cin >> r >> x >> y >> x1 >> y1;
  int d = 2 * r;
  if (x == x1 && y == y1) {
    cout << "0\n";
    return 0;
  }
  float a = x1 - x;
  float b = y1 - y;
  float p = sqrt(a * a + b * b);
  int m = sqrt(a * a + b * b);
  if (p < d) {
    cout << "1";
    return 0;
  } else {
    if (p > m) {
      cout << m / d + 1;
    } else {
      if (m % d == 0) {
        cout << m / d;
      } else {
        cout << m / d + 1;
      }
    }
  }
  return 0;
}
