source_code: import java.util.Scanner;
  
  public class A015 {
  
  	public static void main(String[] args) {
  		Scanner in = new Scanner(System.in);
  		int n = in.nextInt(), t = in.nextInt();
  		int[] centers = new int[n], sides = new int[n];
  		for (int x = 0; x < n; x++) {
  			centers[x] = in.nextInt();
  			sides[x] = in.nextInt();
  		}
  		int count = 0;
  
  		big: for (int x = -4000; x <= 4000; x++) {
  			boolean touch = false;
  			for (int i = 0; i < n; i++) {
  				int d = 2*centers[i] - x;
  				d = d > 0 ? d : -d;
  				int s = t + sides[i];
  				if (s == d) {
  					touch = true;
  				} else if (s > d) {
  					continue big;
  				}
  			}
  			if (touch)
  				count++;
  		}
  		System.out.println(count);
  	}
  }
  