求助巨佬！不知道哪一步错了（悲）的蒟蒻跪谢！

这是蒟蒻不知道哪一步有问题的代码qwq

#include<bits/stdc++.h>

using namespace std;

int n,m;
long long s;
int l[20005],r[20005];
int w[20005],v[20005];
long long pre_w[20005],pre_v[20005];
int maxx=-1,minn=0xfffffff;
long long sum;

bool check(int W)
{
    long long Y=0;
    sum=0;
    memset(pre_w,0,sizeof(pre_w));//?
    memset(pre_v,0,sizeof(pre_v));
    for(int i=1;i<=n;i++)
    {
        if(w[i]>=W)
        {
            pre_w[i]=pre_w[i-1]+1;
            pre_v[i]=pre_v[i-1]+v[i];
        }
        else
        {
            pre_w[i]=pre_w[i-1];
            pre_v[i]=pre_v[i-1];
        }
    }

    for(int i=1;i<=m;i++)
    {
        Y+=(pre_w[r[i]]-pre_w[l[i-1]])*(pre_v[r[i]]-pre_v[l[i-1]]);
    }
    sum=llabs(Y-s);//?
    return Y>s;
}

int main()
{
    cin>>n>>m>>s;
    for(int i=1;i<=n;i++)
    {
        cin>>w[i]>>v[i];
        maxx=max(maxx,w[i]);
        minn=min(minn,w[i]);
    }
    for(int i=1;i<=m;i++)
    {
        cin>>l[i]>>r[i];
    }

    int left=minn-1,right=maxx+2;
    long long ans=0x3f3f3f3f3f3f3f3f;
    while(left<=right)
    {
        int mid=(left+right)/2;
        if(check(mid))
        {
            left=mid+1;
        }
        else
        {
            right=mid-1;
        }
        ans=min(ans,sum);
    }
    cout<<ans<<endl;
    return 0;
}

希望巨佬可以看看，蒟蒻跪谢！