Help needed for Paired Up USACO silver

Debugging Help
#1

Problem Info

2017 Open Contest, Silver, Problem 1, Paired Up

My Work

#include
#include
#include
using namespace std;

typedef long long ll;

int main(){
freopen(“pairup.in”,“r”,stdin);
freopen(“pairup.out”,“w”,stdout);
int n;
cin >> n;
vector<pair<ll,ll>> cows; //time, number
ll in1, in2;
ll total = 0;
ll count = 0;
ll bpos = n-1;
ll tmax = -1;
for(int x=0; x<n; x++){
cin >> in1 >> in2;
total += in1;
cows.push_back({in2,in1});
}
ll br = cows[n-1].second;
sort(cows.begin(),cows.end());

for(int x=0; x<n; x++){
    if(count+cows[x].second<=(total/2)){
        count += cows[x].second;
        ll y = cows[x].second;
        while(y>0){
            tmax = max(tmax,cows[x].first+cows[bpos].first);
            if(y>=br){
                y -= br;
                bpos--;
                br = cows[bpos].second;
            }
            else{
                br -= y;
                y = 0;
            }
            tmax = max(tmax,cows[x].first+cows[bpos].first);
        }
    }
    else{
        ll y = (total/2)-count;
        while(y>0){
            tmax = max(tmax,cows[x].first+cows[bpos].first);
            if(y>=br){
                y -= br;
                bpos--;
                br = cows[bpos].second;
            }
            else{
                br -= y;
                y = 0;
            }
            tmax = max(tmax,cows[x].first+cows[bpos].first);
        }
        break;
    }
}
cout << tmax;

}

What I’ve Tried

I made several small changes to the code. I have tried out several of my own test cases and they work fine. However, this code only works for case 1,5,7. For case 2, it gave a number less than the correct answer.

#2

Please be more specific in “What I’ve Tried.” Also, make sure your code is correctly formatted.

Have you tried this?