2491. Divide Players Into Teams of Equal Skill

class Solution {
public:
    long long dividePlayers(vector<int>& skills) {
        sort(skills.begin(),skills.end());
        int i=0;
        int j=skills.size()-1;
        long long sum=skills[0]+skills[j];
        long long cal=0;
        while(i<j){
            if(sum!=skills[i]+skills[j])
                return -1;
            else
                cal+=skills[i]*skills[j];   
            i++;
            j--;
            
     }   return cal;
    }
};