using System;
using System.Collections;
using System.Collections.Generic;
using System.Numerics;

class TEST{
	static void Main(){
		Sol mySol =new Sol();
		mySol.Solve();
	}
}

class Sol{
	public void Solve(){
		int turn=0;
		int[] Player=new int[2];
		for(int i=0;i<1000;i++){
			var d=rba();
			if((d[0]-1)%(d[1]+1)==0){
				Player[turn^1]++;
				turn^=1;
			}else{
				Player[turn]++;
			}
		}
		Console.WriteLine(Player[0]);
		
		
		
	}

	public Sol(){
	}




	static String rs(){return Console.ReadLine();}
	static int ri(){return int.Parse(Console.ReadLine());}
	static long rl(){return long.Parse(Console.ReadLine());}
	static double rd(){return double.Parse(Console.ReadLine());}
	static String[] rsa(){return Console.ReadLine().Split(' ');}
	static int[] ria(){return Array.ConvertAll(Console.ReadLine().Split(' '),e=>int.Parse(e));}
	static long[] rla(){return Array.ConvertAll(Console.ReadLine().Split(' '),e=>long.Parse(e));}
	static double[] rda(){return Array.ConvertAll(Console.ReadLine().Split(' '),e=>double.Parse(e));}
	static BigInteger[] rba(){return Array.ConvertAll(Console.ReadLine().Split(' '),e=>BigInteger.Parse(e));}
}