Help me in solving P4149 problem

help
,
1

My issue

can you please tell me whats wrong with my code:

My code

#include <bits/stdc++.h>
using namespace std;

int main() {
	// your code goes here
    long t; cin>>t;
    while(t--){
        long n; cin>>n;
        long num_neg=0;
        long long sum=0;
        vector<long long> v;
        while(n--){
            long num; cin>>num;
            if(num<0){
                num_neg++;
                v.push_back(num);
            }
            sum = sum+num;
        }
        if(num_neg==0){
            cout<<sum<<endl;
            continue;
        }
        sort(v.begin(), v.end());
        // for(int i=0; i<v.size(); i++){
        //     cout<<v[i]<<" ";
        // }
        // cout<<endl<<sum;
        // cout<<endl;
        if(v.size()>=2){
            long i=0, j=1;
            while(i<v.size() && j<v.size() && v[i]<0 && v[j]<0){
                // cout<<v[i]<<" "<<v[j];
                sum = sum +(2 * abs(v[i]))+ (2 *abs(v[j]));   
                i= i+2; j=j+2;
                // cout<<" "<<sum<<endl;
            }
            cout<<sum<<endl;
        }
        else{
            cout<<sum<<endl;
        }
        
    }
}

Problem Link: Maximise Sum Practice Coding Problem