1 #include <iostream>
 2 #include <stdio.h>
 3 #include <string.h>
 4 #include <queue>
 5 #include <vector>
 6 #include <algorithm>
 7 
 8 using namespace std;
 9 
10 struct Stop
11 {
12     int dis, fuel;
13     bool operator < (Stop s) const
14     {
15         return fuel < s.fuel;
16     }
17 }truck;
18 
19 bool cmp(Stop a, Stop b)
20 {
21     return a.dis > b.dis;
22 }
23 
24 priority_queue<Stop> que;
25 vector<Stop> v;
26 
27 int N, L, P;
28 bool flag = true;
29 int main()
30 {
31     freopen("in.txt", "r", stdin);
32    scanf("%d", &N);
33    while (N--)
34    {
35        int dis, fuel;
36        Stop tmp;
37        scanf("%d%d", &dis, &fuel);
38        tmp.dis = dis;
39        tmp.fuel = fuel;
40        v.push_back(tmp);
41    }
42    sort(v.begin(), v.end(), cmp);
43    scanf("%d%d", &L, &P);
44    truck.dis = L;
45    truck.fuel = P;
46    int j = 0, ans = 0;
47    for (int i = 0; i < v.size(); i++)
48    if (truck.fuel >= (truck.dis - v[i].dis))
49    {
50        que.push(v[i]);
51    }
52    else
53    {
54        i = i-1;
55        if (!que.empty())//如果还有油可以加
56        {
57             truck.fuel += que.top().fuel;
58             que.pop();
59             ans++;
60        }
61        else
62        {
63            printf("-1\n");//这里之前没有直接 退出 而是去设置flag 可能造成了死循环
64            return 0;
65        }
66    }
67     while(flag)
68     {
69         if (truck.dis <= truck.fuel) break;
70         else if (!que.empty())
71         {
72             truck.fuel += que.top().fuel;
73             que.pop();
74             ans++;
75         }
76         else flag = false;
77     }
78    if (flag) printf("%d\n", ans);
79    else printf("-1\n");
80    return 0;
81 }