#include <iostream>
#include <fstream>
 
int main()
{
    int board[10][10] = {0};
 
    std::ifstream input("input.txt");
 
    int n;
    int x, y;
 
    input >> n;
 
    for (int i = 0; i < n; ++i)
    {
        input >> x >> y;
 
        board[x][y] = 1;
    }
 
    input.close();
 
    int p = 0;
 
    for (int i = 1; i < 9; ++i)
    {
        for (int j = 1; j < 9; ++j)
        {
            if (board[i][j] == 1)
            {
                if (board[i - 1][j] == 0)
                    ++p;
 
                if (board[i][j + 1] == 0)
                    ++p;
 
                if (board[i + 1][j] == 0)
                    ++p;
 
                if (board[i][j - 1] == 0)
                    ++p;
            }
        }
    }
 
    std::ofstream output("output.txt");
 
    output << p;
 
    output.close();
 
    return 0;