思路：

构造。

实现：

 1 #include<bits/stdc++.h>
 2 using namespace std;
 3  
 4 int main()
 5 {
 6     int n;
 7     while (cin >> n)
 8     {
 9         cout << 3 * n + 4 << endl;
10         int x = 0, y = 0;
11         cout << x + 1 << " " << y << endl;
12         cout << x << " " << y + 1 << endl;
13         cout << x + 1 << " " << y + 1 << endl;
14         for (int i = 0; i < n; i++)
15         {
16             cout << x << " " << y << endl; 
17             cout << x - 1 << " " << y << endl;
18             cout << x << " " << y - 1 << endl;
19             x--; y--;
20         }
21         cout << x << " " << y << endl;
22     }
23     return 0;    
24 }