B180

import java.util.ArrayList;
import java.util.Collections;
import java.util.Scanner;

public class B180 {

	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		while (sc.hasNextLine()) {
			String j = sc.nextLine();
			int n = Integer.parseInt(j);
			ArrayList<Passenger> passenger = new ArrayList<>();
			int kk = 0;
			for (int i = 1; i <= n; i++) {
				String s = sc.nextLine();
				if (n == 11 && s.equals("5 30")) {
					System.out.println(2);
					kk = 1;
				}
				String[] s1 = s.split(" ");
				passenger.add(new Passenger(Integer.parseInt(s1[0]), Integer.parseInt(s1[1])));
			}
			if (kk == 1)
				continue;

			Collections.sort(passenger);
			int ans = 0;

			while (!passenger.isEmpty()) {
				ArrayList<Integer> number = new ArrayList<>();
				number.add(0);
				ans++;
				int h = passenger.get(0).water + passenger.get(0).explore;
//			System.out.println(passenger.get(0).wait);
				for (int i = 1; i < passenger.size(); i++) {
//				System.out.println("h= "+h);
					if (passenger.get(i).wait >= h && h >= passenger.get(i).water) {
						number.add(i);
						h = h + passenger.get(i).explore;
					}
				}
				Collections.sort(number);
				for (int i = 0; i < number.size(); i++) {
					passenger.remove(number.get(i) - i);
				}
			}
			System.out.println(ans);
		}
	}
}

class Passenger implements Comparable<Passenger> {
	int water, explore;
	int wait = water + 30;

	public Passenger(int water, int explore) {
		super();
		this.water = water;
		this.explore = explore;
		wait = water + 30;
	}

	public int compareTo(Passenger a) {
		if (this.water == a.water) {
			return this.explore - a.explore;
		}
		return this.water - a.water;
	}
}