wi<=1e5为什么用int存就会wa

#include <bits/stdc++.h>
using namespace std;
#define ll long long
#define endl '\n'
#define mod 1024523
#define fi first
#define se second
#define please return
#define AC 0
int main() 
{
    ios::sync_with_stdio(false);
  	cin.tie(nullptr);
	ll n;
	cin>>n;
	vector<int> a(2*n,0);
	for(ll i=0;i<2*n;i++)
	{
		cin>>a[i];
	}
	sort(a.begin(),a.end());
	ll left=0,right=2*n-1;
	ll ans=0;
	while(left<right)
	{
		ans+=(a[left]*a[right]);
		left++;
		right--;
	}
	cout<<ans;
    please AC;
}