求救，为何，前四个点都AC了，最后一个点却RE

#include<bits/stdc++.h>
using namespace std;
struct apple
{
    int x,y;
}app[6000];

bool com_x(apple a,apple b)   { return a.x<=b.x; }
bool com_y(apple a,apple b)   { return a.y<=b.y; }

int main()
{
    int n,s,a,b;
    cin>>n>>s>>a>>b;
    if(!n) return 0*printf("0");
    for(int i=0;i<n;i++)    cin>>app[i].x>>app[i].y;
    sort(app,app+n,com_x);
    for(int i=0;i<n;i++)    if(app[i].x>a+b) { n=i; break; }
    sort(app,app+n,com_y);
    int i=0;
    do
    {
       s=s-app[i++].y;
    }while(s>=0);
    cout<<i-1;
}