为啥会RE，求大佬帮助（蒟蒻也行）

#include<iostream>
#include<algorithm>
using namespace std;
struct apple
{
    int high;
    int energy;       
};
apple a[5005];
bool cmp(apple x,apple y)
{
    if(x.energy<=y.energy)  return true;
    return false;    
}
int main()
{
    int n,s,i;
    int sum=0;
    cin>>n>>s;
    int c,b;
    cin>>c>>b;
    b+=c;
    for(i=1;i<=n;i++)
      cin>>a[i].high>>a[i].energy;
    sort(a+1,a+n+1,cmp);
    for(i=1;i<=n;i++)
    {
        if(s-a[i].energy<0)  break;
        if(b<a[i].high)  continue;
        sum++;
        s-=a[i].energy;                 
    }
    cout<<sum<<endl;
    return 0;
}