import java.awt.Point;
import java.io.File;
import java.io.FileNotFoundException;
import java.io.PrintWriter;
import java.util.Scanner;

public class Main {
    private Scanner scan;

    public void run() throws FileNotFoundException {
        scan = new Scanner(new File("./mowing.in"));
        int n, t;
        n = scan.nextInt();
        t = scan.nextInt();

        Point coords[] = new Point[ n ];
        for( int i = 0; i < n; i++ )
        {
            coords[i] = new Point();
            coords[i].x = scan.nextInt();
            coords[i].y = scan.nextInt();
        }

        int fh = (coords[0].y == coords[1].y) ? 1 : 0;

        int ANS = 0;

        for( int i = n-1; i > 0; i-- )
        {
            for( int j = i-t-1; j > 0; j-- )
            {
                if( i % 2 == fh ) // if horiz
                {
                    int bigx = Math.max( coords[i].x, coords[i-1].x );
                    int smallx = Math.min( coords[i].x, coords[i-1].x );
                    int bigy = Math.max( coords[j].y, coords[j-1].y );
                    int smally = Math.min( coords[j].y, coords[j-1].y );

                    if( coords[i].y > smally && coords[i].y < bigy &&
                        coords[j].x > smallx && coords[j].x < bigx )
                    {
                        ANS++;
                    }
                } else // if vert
                {
                    int bigy = Math.max( coords[i].y, coords[i-1].y );
                    int smally = Math.min( coords[i].y, coords[i-1].y );
                    int bigx = Math.max( coords[j].x, coords[j-1].x );
                    int smallx = Math.min( coords[j].x, coords[j-1].x );

                    if( coords[j].y > smally && coords[j].y < bigy &&
                        coords[i].x > smallx && coords[i].x < bigx )
                    {
                        ANS++;
                    }
                }
            }
        }

        PrintWriter pw = new PrintWriter(new File("./mowing.out"));
        pw.println( ANS );
        pw.close();
        scan.close();
    }

    public static void main(String[] args) {
        Main main = new Main();
        try {
            main.run();
        } catch (FileNotFoundException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
    }
}