unsatisfied barton

#include<bits/stdc++.h>
using namespace std;
typedef long long ll;

void print(priority_queue<pair<ll,ll>> p)
{
    while(!p.empty())
    {
        cout<<p.top().first<<" -> "<<p.top().second<<endl;
        p.pop();
    }
}

ll like(vector<ll> a)
{

    priority_queue<pair<ll,ll>> p;
    ll count=0; ll num=-1;
    for(ll i=0;i<a.size()-1;i++)
    {
        if(a[i]==a[i+1])
        { count++; num=a[i];}
        else
        {
           if(count!=0) p.push(make_pair(count,num));
            count=0; num=-1;
        }
    }
    if(count!=0)
    p.push(make_pair(count,num));

    //print(p);

    pair<ll,ll> x,y;
    priority_queue<pair<ll,ll>> q;
    ll sum=0;
    while(p.size()>=2)
    {
         x = p.top(); p.pop();
         y = p.top(); p.pop();
        if(x.second!=y.second)
        {
            if(x.first > y.first)
            { sum+=y.first; x.first-=y.first; p.push(x); }
            else if(y.first > x.first)
            { sum+=x.first; y.first-=x.first; p.push(y); }
            else
            { sum+=x.first; }
        }
        else
        {
            p.push(y);
            if(q.empty() || q.top().second==x.second) q.push(x);
            else
            {
                y=q.top(); q.pop();
                if(x.first > y.first)
                { sum+=y.first; x.first-=y.first; p.push(x); }
                else if(y.first > x.first)
                { sum+=x.first; y.first-=x.first; p.push(y); }
                else
                { sum+=x.first; }
            }
        }
    }
    if(p.size()==1)
    {
        if(q.empty() || p.top().second==q.top().second) { sum+=p.top().first; p.pop(); }
        else
        {
            x=p.top(); p.pop();
            y=q.top(); q.pop();
            if(x.first > y.first)
            { sum+=y.first; x.first-=y.first; q.push(x); }
            else if(y.first > x.first)
            { sum+=x.first; y.first-=x.first; q.push(y); }
            else
            { sum+=x.first; }
        }
    }
    while(!q.empty())
    {
        sum+=q.top().first; q.pop();
    }

    return sum;
}

bool impossible(vector<ll> a)
{
    sort(a.begin(),a.end());
    ll n=a.size();

    ll count=0; ll mx=0;
    for(ll i=0;i<n-1;i++)
    {
        if(a[i]==a[i+1]) count++;
        else count=0;

        if(count>mx) mx=count;
    }

    mx++;
    if(n%2==0 && mx>n/2) return true;

    if(n%2==1 && mx > n/2 +1) return true;

    return false;
}

int main()
{
    ios_base::sync_with_stdio(0);
    cout.tie(0);  cin.tie(0);

    ll n; cin>>n;
    vector<ll> a(n);
    for(ll i=0;i<n;i++) cin>>a[i];

    if(impossible(a))
    {cout<<-1<<endl; return 0;}

    cout<<like(a)<<endl;
}