#include<vector>
#include<algorithm>
#include<iostream>
using namespace std;

int calcola(vector<int> a){
int t=1;
int u=0;
while(t<a.size()){t=t*2;}
for(int i=0;i<t-a.size();i++){a.push_back(200000000);}
int k=2;
while(k<=t){
for(int i=0;i<t;i=i+k){
int b=0;
for(int n=0;n<k/2;n++){
  if(a[i+n]>a[i+k/2+b]){u=u+k/2-n;n--;b++;if(b>=k/2){n=k/2;}}
}
sort(a.begin()+i,a.begin()+i+k);

}


k=k*2;}


  return u;
}







long long paletta_sort(int N, int V[]) {

vector<int> s1;
  vector<int> s2;

  for(int i=0;i<N;i++){
    if(i%2==0){
      s1.push_back(V[i]);
    }else{s2.push_back(V[i]);}
  }

N=calcola(s1)+calcola(s2);

for(int i=0;i<N;i=i+2){
  if(s2[i+1]<s1[i]){N=-1;}
}


  
    return N;
}

/*
int main(){

vector<int> s={2,3,0,5,4,1};
  cout<<calcola(s);


  cout<<paletta_sort(6,s)


  return 0;
}
*/