#include <bits/stdc++.h>
using namespace std;
int main() {
  int t, i, j, k, x, y, x1, x2, y1, y2;
  cin >> k >> x1 >> y1 >> x2 >> y2;
  i = ceil(sqrt(pow(x1 - x2, 2) + pow(y1 - y2, 2)));
  if (x1 == x2 && y1 == y2)
    cout << 0;
  else {
    cout << i / 2 * k;
  }
}
