#include  "pch.h"
#include <iostream>
#include <stdio.h>


int main()
{
    const int RMB[] = { 200, 100, 20, 5, 1 };
    const int NUM = 5;
    int X = 628;
    int count = 0;
    for (int i = 0; i < NUM; i++) {
        int use = X / RMB[i];
        count += use;
        X = X - RMB[i] * use;
        printf("需要面额为%d的%d张, ", RMB[i], use);
        printf("剩余需要支付金额%d.\n", X);
    }
    printf("总共需要%d张\n", count);
    return 0;
}

class Solution {
public:
    int wiggleMaxLength(std::vector<int>& nums) {
        if (nums.size()< 2)
        {
            return nums.size();
        }
        static const int BEGIN = 0;
        static const int UP = 1;
        static const int DOWN = 2;
        int STATE = BEGIN;
        int max_length = 1;
        for (int i =1; i < nums.size(); i++){
            switch(STATE){
                case BEGIN:
                    if(nums[i-1] < nums[i]){
                        STATE = UP;
                        max_length++;
                    }
                    else if (nums[i-1] > nums[i]){
                        STATE = DOWN;
                        max_length++;
                    }
                    break;
                case UP:
                    if(nums[i-1] > nums[i]){
                        STATE = DOWN;
                        max_length++;
                    }
                    break;
                case DOWN:
                    if(nums[i-1] < nums[i]){
                        STATE = UP;
                        max_length++;
                    }
                    break;
            }
        }
        return max_length++;
    }
};

class Solution {
public:
    string removeKdigits(string num, int k) {
        std::vector<int> S;   //S是整型数组，当栈用
        std::string result = "";
        for (int i = 0 ; i < num.length(); i++)
        {
            int number = num[i] - ‘0‘; //字符型num转化为整数
            while (S.size() != 0 && S[S.size() -1] > number && k > 0){
                S.pop_back();
                k--;
            }
            if(number != 0 || S.size() != 0){
                S.push_back(number);
            }
        }
        while (S.size() != 0 && k > 0 ) 
        {
            S.pop_back();
            k--;
        }
        for(int i = 0; i < S.size(); i++)
        {
            result.append(1, ‘0‘ + S[i]); //将整数转化为字符
        }
        if(result == ""){
            result = "0";
        }
        return result;
    }
};

class Solution {
public:
    bool canJump(vector<int>& nums) {
        std::vector<int> index;
        for(int i = 0; i < nums.size(); i++)
        {
            index.push_back(i + nums[i]);
        }
        int jump = 0;
        int max_index = index[0];
        while(jump < nums.size() && jump <= max_index)
        {
            if(max_index < index[jump])
            {
                max_index = index[jump];
            }
            jump++;
        }
        if(jump == nums.size())
        {
            return true;
        }
        return false;
    }
};

#define _CRT_SECURE_NO_WARNINGS
#include  "pch.h"
#include <iostream>
#include <stdio.h>
#include <queue>
#include <algorithm>


bool cmp(const std::pair<int, int> &a, const std::pair<int, int> &b) {
    return a.first > b.first;
}
int get_minimum_stop(int L, int P, std::vector<std::pair<int, int> > &stop) 
{
    std::priority_queue<int> Q;
    int result = 0;
    stop.push_back(std::make_pair(0, 0));
    std::sort(stop.begin(), stop.end(), cmp);
    for (int i = 0; i < stop.size(); i++) 
    {
        int dis = L - stop[i].first;
        while ( !Q.empty() && P < dis) {
            P += Q.top();
            Q.pop();
            result++;
        }
        if (P < dis && Q.empty()) {
            return -1;
        }
        P = P - dis;
        L = stop[i].first;
        Q.push(stop[i].second);
    }
    return result;
}


int main()
{
    std::vector<std::pair<int, int> >stop;
    int N;
    int L;
    int P;
    int distance;
    int fuel;
    scanf("%d", &N);
    for (int i = 0; i < N; i++) {
        scanf("%d %d", &distance, &fuel);
        stop.push_back(std::make_pair(distance, fuel));
    }
    scanf("%d %d", &L, &P);
    printf("%d\n", get_minimum_stop(L, P, stop));
    return 0;
}