#include<stdio.h>#include<queue>#include<algorithm>using namespace std;struct stop{ int x; int v;}s[10010];bool comp(stop s1, stop s2){ return s1.x < s2.x;}int main(){ int n, i, L, P; while(~scanf("%d",&n)) { for(i = 0; i < n; i++) scanf("%d%d",&s[i].x, &s[i].v); scanf("%d%d",&L,&P); for(i = 0; i < n; i++) s[i].x = L - s[i].x; s[n].x = L; s[n++].v = 0; sort(s, s+n, comp); priority_queue<int, vector<int>, less<int> > Q; int rest = P; int ans = 0; int pos = 0; for(i = 0; i < n; i++) { int dis = s[i].x - pos; while(rest - dis < 0) { if(Q.empty()) { ans = -1; break; } rest += Q.top(); Q.pop(); ans++; } if(ans == -1) break; rest = rest - dis; pos = s[i].x; Q.push(s[i].v); } printf("%dn",ans); } return 0;}
