Problem Statement

We have an infinite hexagonal grid shown below. Initially, all squares are white.

A hexagonal cell is represented as (i,j) with two integers i and j.
Cell (i,j) is adjacent to the following six cells:

• (i-1,j-1)
• (i-1,j)
• (i,j-1)
• (i,j+1)
• (i+1,j)
• (i+1,j+1)

Takahashi has painted $N cells (X_1,Y_1),(X_2,Y_2),\dots,(X_N,Y_N)$ black.
Find the number of connected components formed by the black cells.
Two black cells belong to the same connected component when one can travel between those two black cells by repeatedly moving to an adjacent black cell.

Input

The input is given from Standard Input in the following format:
N
X_1 Y_1
X_2 Y_2
$\vdots$
X_N Y_N

Output

Print the answer as an integer.

Constraints

• All values in the input are integers.
• $1 \le N \le 1000$
• $|X_i|,|Y_i| \le 1000$
• The pairs (X_i,Y_i) are distinct.

Sample Input 1

6
-1 -1
0 1
0 2
1 0
1 2
2 0

Sample Output 1

3

After Takahashi paints cells black, the grid looks as shown below.

The black squares form the following three connected components:

• (-1,-1)
• (1,0),(2,0)
• (0,1),(0,2),(1,2)

Sample Input 2

4
5 0
4 1
-3 -4
-2 -5

Sample Output 2

4

Sample Input 3

5
2 1
2 -1
1 0
3 1
1 -1

Sample Output 3

1

见题面 Input 部分

见题面 Output 部分