#include<bits/stdc++.h>
using namespace std;
#define ll long long
const int SZ=1<<20;
char buf[SZ],*p1,*p2;
#define gc() (p1==p2&&(p2=(p1=buf)+fread(buf,1,SZ,stdin),p1==p2)?EOF:*p1++)
ll read(){
	ll n=0; bool m=0;
	char c=gc();
	while(c<'0'||c>'9')m=c=='-',c=gc();
	while(c>='0'&&c<='9')n=(n<<3)+(n<<1)+(c^'0'),c=gc();
	return m?-n:n;
}
const int N=500005;
const ll inf=0x3f3f3f3f3f3f3f3f;
int n,p[N],tp,q[N],tq,cur;
ll f[2][N],pre[N],suf[N],sp[N],sq[N];
struct node{int x,i;}a[N];
bool cmp(node x,node y){return abs(x.x)<abs(y.x)||abs(x.x)==abs(y.x)&&x.i<y.i;}
int b[N];
void upd(int x,int y){
	while(x<=n)b[x]+=y,x+=x&-x;
}
int ask(int x){
	int y=0;
	while(x)y+=b[x],x-=x&-x;
	return y;
}
void solve(int r,int X){
	// for(int i=1;i<=tp;i++)printf("%d ",p[i]);
	// printf("p\n");
	// for(int i=1;i<=tq;i++)printf("%d ",q[i]);
	// printf("q\n");
	int i=0,j=0,k=0,op=1,pi=0,pj=0;
	while(1){
		k++;
		if(op){
			if(i==tp)break;
			i++;
			while(pj<j&&q[pj+1]<p[i])pj++;
			pre[k]=pre[k-1]+(p[i]-1)-(i-1)-pj;
		}else{
			if(j==tq)break;
			j++;
			while(pi<i&&p[pi+1]<q[j])pi++;
			pre[k]=pre[k-1]+(q[j]-1)-(j-1)-pi;
		}
		op^=1;
	}
	i=tp+1,j=tq+1,k=tp+tq+1,op=!(r&1),pi=tp+1,pj=tq+1,suf[k]=0;
	while(1){
		k--;
		if(op){
			if(i==1)break;
			i--;
			while(pj>j&&q[pj-1]>p[i])pj--;
			suf[k]=suf[k+1]+(r-p[i])-(tp-i)-(tq+1-pj);
		}else{
			if(j==1)break;
			j--;
			while(pi>i&&p[pi-1]>q[j])pi--;
			suf[k]=suf[k+1]+(r-q[j])-(tq-j)-(tp+1-pi);
		}
		op^=1;
	}
	for(i=1,j=0;i<=tp;i++){
		while(j<tq&&q[j+1]<p[i])j++;
		sp[i]=sp[i-1]+j;
	}
	for(j=1,i=0;j<=tq;j++){
		while(i<tp&&p[i+1]<q[j])i++;
		sq[j]=sq[j-1]+i;
	}
	i=0,j=0,k=0,op=1,pi=0,pj=0;
	int rp=tp-i,rq=tq-j;
	if(rp==rq||(r&1)&&rp+1==rq||!(r&1)&&rp==rq+1){
		ll x=pre[k]+suf[k+1];
		if(p[i]<q[j])x-=sq[j]-sq[pj];
		else x-=sp[i]-sp[pi];
		// printf(">>%d %lld\n",k,x);
		f[X][cur]=min(f[X][cur],f[X^(k&1)][cur-1]+x);
	}
	while(1){
		k++;
		if(op){
			if(i==tp)break;
			i++;
			while(pj<tq&&q[pj+1]<p[i])pj++;
		}else{
			if(j==tq)break;
			j++;
			while(pi<tp&&p[pi+1]<q[j])pi++;
		}
		rp=tp-i,rq=tq-j;
		if(rp==rq||(r&1)&&rp+1==rq||!(r&1)&&rp==rq+1){
			ll x=pre[k]+suf[k+1];
			if(p[i]<q[j])x-=sq[j]-sq[pj];
			else x-=sp[i]-sp[pi];
			// printf(">>%d %lld\n",k,x);
			f[X][cur]=min(f[X][cur],f[X^(k&1)][cur-1]+x);
		}
		op^=1;
	}
}
int main(){
	n=read();
	for(int i=1;i<=n;i++){
		a[i].x=read(),a[i].i=i;
		if(i&1)a[i].x=-a[i].x;
	}
	stable_sort(a+1,a+n+1,cmp);
	for(int l=1,r=1;l<=n;l=r=r+1){
		while(r<n&&abs(a[l].x)==abs(a[r+1].x))r++;
		for(int i=l;i<=r;i++)upd(a[i].i,1);
		if(a[l].x==0)continue;
		cur++,f[0][cur]=f[1][cur]=inf;
		tp=tq=0;
		for(int i=l;i<=r;i++){
			if(a[i].x>0)p[++tp]=ask(a[i].i);
			else q[++tq]=ask(a[i].i);
		}
		solve(r,0);
		tp=tq=0;
		for(int i=l;i<=r;i++){
			if(a[i].x<0)p[++tp]=ask(a[i].i);
			else q[++tq]=ask(a[i].i);
		}
		solve(r,1);
		// printf("%lld %lld\n",f[0][cur],f[1][cur]);
	}
	ll ans=min(f[0][cur],f[1][cur]);
	printf("%lld",ans==inf?-1:ans);
	return 0;
}