> #include<iostream>
> #include<cstdio>
> #include<cstring>
> #include<cmath>
> #include<algorithm>
> #include<queue>
> using namespace std;
> int l,p,n;
> pair<int,int>pa[10005];
> bool cmp(pair<int,int> a,pair<int,int> b){
> 	return a.first<b.first;
> }
> void solve(){
> 	pa[n].first=l;
> 	pa[n].second=0;
> 	n++;
> 	priority_queue<int>que;
> 	int ans=0,pos=0,tank=p;
> 	for(int i=0;i<n;i++){
> 		int d=pa[i].first-pos;
> 		while(tank-d<0){
> 			if(que.empty()){
> 				puts("-1");
> 				return;
> 			}
> 			tank+=que.top();
> 			que.pop();
> 			ans++;
> 		}
> 		tank-=d;
> 		pos=pa[i].first;
> 		que.push(pa[i].second);
> 	}
> 	printf("%d\n",ans);
> }
> int main(){
> 	scanf("%d",&n);
> 	for(int i=0;i<n;i++)
> 		scanf("%d%d",&pa[i].first,&pa[i].second);
> 	scanf("%d%d",&l,&p);
> 	for(int i=0;i<n;i++)	pa[i].first=l-pa[i].first;
> 	sort(pa,pa+n,cmp);
> 	solve();
> }