#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef pair<ll,ll> P;
typedef vector<ll> vi;
typedef vector<vi> vvi;
typedef vector<P> vp;
typedef vector<vp> vvp;
#define rep(i,n) for(ll i=0;i<(ll)(n);i++)
#define REP(i,k,n) for(ll i=(ll)(k);i<(ll)(n);i++)
#define all(a) a.begin(),a.end()
#define fi first
#define se second
#define pb emplace_back
#define dupli(a) {sort(all(a));a.erase(unique(all(a)),a.end());}
#define lb(v,k) (lower_bound(all(v),k)-v.begin())
template<class T> bool chmin(T&a,T b){if(a>b){a=b;return true;}return false;}
template<class T> bool chmax(T&a,T b){if(a<b){a=b;return true;}return false;}
template<class T> void out(T a){cout<<a<<'\n';}
template<class T> void outv(T v){rep(i,v.size()){if(i)cout<<' ';cout<<v[i];}cout<<'\n';}
template<class T> void outvv(T v){for(auto x:v)outv(x);}
const ll inf=1001001001001001001;
struct BIT{
    ll n;
    vi bit;
    BIT(ll n_):n(n_),bit(n_+1){}
    void add(ll i){
        bit[i]++;
    }
    ll get(ll l,ll r){
        ll res=0;
        REP(i,l,r)res+=bit[i];
        return res;
    }
};
int main(){
    ll n;cin>>n;
    vi v(n);rep(i,n)cin>>v[i];
    rep(i,n)if(i&1)v[i]*=-1;
    vi srt(n);
    rep(i,n)srt[i]=abs(v[i]);
    dupli(srt);
    vvi g(srt.size());
    rep(i,n)g[lb(srt,abs(v[i]))].pb(i);
    vvi dp(srt.size(),vi(2,inf));
    BIT bit(n);
    rep(i,srt.size()){
        if(srt[i]==0){
            rep(j,2)dp[i][j]=0;
        }
        else{
            vvi S(2);
            for(ll j:g[i])S[(int)(v[j]>0)].pb(j);
            rep(k,2){
                vvi table(2,vi(g[i].size()+1,inf));
                vvi cnt(2,vi(g[i].size()+1));
                {
                    table[0][0]=0;
                    vi c(2);
                    rep(j,g[i].size()){
                        ll f=(j+k)&1;
                        cnt[0][j+1]=cnt[0][j]+f;
                        if(S[f].size()==c[f])break;
                        ll x=S[f][c[f]++];
                        table[0][j+1]=table[0][j]+bit.get(0,x)+max(0ll,lb(S[f^1],x)-c[f^1]);
                    }
                }
                {
                    ll s=bit.get(0,n)+g[i].size();
                    table[1][0]=0;
                    vi c(2);rep(j,2)c[j]=S[j].size()-1;
                    rep(j,g[i].size()){
                        ll f=(j+s+k)&1;
                        cnt[1][j+1]=cnt[1][j]+f;
                        if(c[f]<0)break;
                        ll x=S[f][c[f]--];
                        table[1][j+1]=table[1][j]+bit.get(x+1,n)+max(0ll,c[f^1]+1-lb(S[f^1],x));
                    }
                }
                rep(j,g[i].size()+1)if(cnt[0][j]+cnt[1][g[i].size()-j]==S[1].size())chmin(dp[i][k],table[0][j]+table[1][g[i].size()-j]+((i==0) ? 0 : dp[i-1][(j+k)&1]));
            }
        }
        for(ll j:g[i])bit.add(j);
    }
    // outvv(dp);
    out(dp[srt.size()-1][0]>inf/2 ? -1 : dp[srt.size()-1][0]);
}