【CodeForces 717C】Potions Homework

#include <cstdio>
#include <algorithm>
#define ll long long
using namespace std;
int a[100001];
int main(){
    int n,ans=0;
    scanf("%d",&n);
    for(int i=1;i<=n;++i)
        scanf("%d",&a[i]);
    sort(a+1,a+1+n);
    for(int i=1;i<=n;++i)
        ans=(ans+(ll)a[i]*a[n-i+1]%10007)%10007;
    printf("%d",ans);
    return 0;
}