This submission is migrated from previous version of oj.uz, which used different machine for grading. This submission may have different result if resubmitted.
#include<bits/stdc++.h>
using namespace std;
#define int long long
#define pb push_back
int a[5005];
signed main()
{
    int n;
    cin>>n;
    for(int i=0;i<n;i++)
    {
        int x;
        cin>>x;
        a[x]++;
    }
    int ans=0;
    for(int i=1;i<=4000;i++)
    {
        for(int j=i;j<=4000;j++)
        {
            if(!a[i]||!a[j]) continue;
            if(i==j&&(a[i]*(a[j]+1)/2)%2==0) continue;
            if(i!=j&&((a[i]*a[j])%2==0)) continue;
            ans^=(i+j);
        }
    }
    cout<<ans<<endl;
}
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