Problem:
Score : 700 points

Problem Statement

In the final of CODE FESTIVAL in some year, there are N participants.
The height and power of Participant i is H_i and P_i, respectively.

Ringo is hosting a game of stacking zabuton (cushions).

The participants will line up in a row in some order, and they will in turn try to add zabuton to the stack of zabuton.
Initially, the stack is empty.
When it is Participant i's turn, if there are H_i or less zabuton already stacked, he/she will add exactly P_i zabuton to the stack. Otherwise, he/she will give up and do nothing.

Ringo wants to maximize the number of participants who can add zabuton to the stack.
How many participants can add zabuton to the stack in the optimal order of participants?

Constraints

1 \leq N \leq 5000

0 \leq H_i \leq 10^9

1 \leq P_i \leq 10^9

Input

Input is given from Standard Input in the following format:

N
H_1 P_1
H_2 P_2
:
H_N P_N

Output

Print the maximum number of participants who can add zabuton to the stack.

Sample Input 1

3
0 2
1 3
3 4

Sample Output 1

2

When the participants line up in the same order as the input, Participants 1 and 3 will be able to add zabuton.

On the other hand, there is no order such that all three participants can add zabuton. Thus, the answer is 2.

Sample Input 2

3
2 4
3 1
4 1

Sample Output 2

3

When the participants line up in the order 2, 3, 1, all of them will be able to add zabuton.

Sample Input 3

10
1 3
8 4
8 3
9 1
6 4
2 3
4 2
9 2
8 3
0 1

Sample Output 3

5

Solution in Java8 (OpenJDK 1.8.0) (judge verdict: Accepted)

import java.io.OutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.util.Arrays;
import java.util.PriorityQueue;
import java.io.IOException;
import java.io.UncheckedIOException;
import java.io.Closeable;
import java.io.Writer;
import java.io.OutputStreamWriter;
import java.io.InputStream;

/**
 * Built using CHelper plug-in Actual solution is at the top
 * 
 * @author daltao
 */
public class Main {
    public static void main(String[] args) throws Exception {
        Thread thread = new Thread(null, new TaskAdapter(), "daltao", 1 << 27);
        thread.start();
        thread.join();
    }

    static class TaskAdapter implements Runnable {
        @Override
        public void run() {
            InputStream inputStream = System.in;
            OutputStream outputStream = System.out;
            FastInput in = new FastInput(inputStream);
            FastOutput out = new FastOutput(outputStream);
            Zabuton solver = new Zabuton();
            solver.solve(1, in, out);
            out.close();
        }
    }
    static class Zabuton {
        public void solve(int testNumber, FastInput in, FastOutput out) {
            int n = in.readInt();
            Participant[] ps = new Participant[n];
            for (int i = 0; i < n; i++) {
                ps[i] = new Participant();
                ps[i].h = in.readInt();
                ps[i].p = in.readInt();
            }

            PriorityQueue<Participant> pq = new PriorityQueue<>(n, (a, b) -> -(a.p - b.p));

            int used = 0;
            Arrays.sort(ps, (a, b) -> Integer.compare(a.h + a.p, b.h + b.p));
            for (Participant p : ps) {
                if (used <= p.h) {
                    used += p.p;
                    pq.add(p);
                } else {
                    if (pq.peek().p >= p.p) {
                        used -= pq.poll().p;
                        used += p.p;
                        pq.add(p);
                    }
                }
            }

            out.println(pq.size());
        }

    }
    static class Participant {
        int h;
        int p;

    }
    static class FastInput {
        private final InputStream is;
        private byte[] buf = new byte[1 << 13];
        private int bufLen;
        private int bufOffset;
        private int next;

        public FastInput(InputStream is) {
            this.is = is;
        }

        private int read() {
            while (bufLen == bufOffset) {
                bufOffset = 0;
                try {
                    bufLen = is.read(buf);
                } catch (IOException e) {
                    bufLen = -1;
                }
                if (bufLen == -1) {
                    return -1;
                }
            }
            return buf[bufOffset++];
        }

        public void skipBlank() {
            while (next >= 0 && next <= 32) {
                next = read();
            }
        }

        public int readInt() {
            int sign = 1;

            skipBlank();
            if (next == '+' || next == '-') {
                sign = next == '+' ? 1 : -1;
                next = read();
            }

            int val = 0;
            if (sign == 1) {
                while (next >= '0' && next <= '9') {
                    val = val * 10 + next - '0';
                    next = read();
                }
            } else {
                while (next >= '0' && next <= '9') {
                    val = val * 10 - next + '0';
                    next = read();
                }
            }

            return val;
        }

    }
    static class FastOutput implements AutoCloseable, Closeable {
        private StringBuilder cache = new StringBuilder(10 << 20);
        private final Writer os;

        public FastOutput(Writer os) {
            this.os = os;
        }

        public FastOutput(OutputStream os) {
            this(new OutputStreamWriter(os));
        }

        public FastOutput println(int c) {
            cache.append(c).append('\n');
            return this;
        }

        public FastOutput flush() {
            try {
                os.append(cache);
                os.flush();
                cache.setLength(0);
            } catch (IOException e) {
                throw new UncheckedIOException(e);
            }
            return this;
        }

        public void close() {
            flush();
            try {
                os.close();
            } catch (IOException e) {
                throw new UncheckedIOException(e);
            }
        }

    }
}