#include<bits/stdc++.h>
using namespace std;
int h[500005],hh[500005];
vector<int>g[500005][2];
long long f[500005][2];
long long qz[500005],hz[500005];
int A1[500005],A2[500005];
int B1[500005],B2[500005];
int main(){
	int n;
	scanf("%d",&n);
	for(int i=1;i<=n;++i)scanf("%d",&h[i]),h[i]*=(i%2?-1:1);
	int gs=0,tt=0;
	for(int i=1;i<=n;++i){
		if(!h[i])++gs,g[h[i]][0].emplace_back(i);
		else hh[++tt]=abs(h[i]);
	}
	sort(hh+1,hh+tt+1);
	tt=unique(hh+1,hh+tt+1)-hh-1;
	for(int i=1;i<=n;++i)if(h[i]){
		int w=lower_bound(hh+1,hh+tt+1,abs(h[i]))-hh;
		h[i]=(h[i]>0?1:-1)*w;
		g[abs(h[i])][h[i]>0].emplace_back(i);
	}
	memset(f,63,sizeof(f));
	f[tt+1][0]=0;
	int he=0;
	for(int i=tt;i>=1;--i){
		int A=g[i][0].size(),B=g[i][1].size();
		for(int j=0;j<2;++j){
			qz[0]=hz[A+B+1]=0;
			for(int k=1;k<=A+B;++k)qz[k]=hz[k]=2e18;
			int b1=0,b2=0;
			vector<int>v1,v2;
			A1[0]=B1[0]=A2[A+B+1]=B2[A+B+1]=0;
			for(int k=1;k<=A+B;++k){
				int x=0;
				A1[k]=A1[k-1],B1[k]=B1[k-1];
				if((j+k)%2==0){
					if(b1==A)break;
					x=g[i][0][b1++];++A1[k];
				}else{
					if(b2==B)break;
					x=g[i][1][b2++];++A2[k];
				}
				int gs=0;
				for(int I=1;I<x;++I)if(abs(h[I])<=i)++gs;
				for(auto cu:v1){
					if(cu<x)--gs;
					else ++gs;
				}
				v1.emplace_back(x);
				qz[k]=qz[k-1]+gs;
			}
			b1=A-1,b2=B-1;
			int jj=he-j;
			for(int k=A+B;k>=1;--k){
				A2[k]=A2[k+1],B2[k]=B2[k+1];
				int x=0;
				if((n-jj-(A+B-k))%2==1){
					if(b1<0)break;
					x=g[i][0][b1--];++A2[k];
				}else{
					if(b2<0)break;
					x=g[i][1][b2--];++B2[k];
				}
				int gs=0;
				for(int I=x+1;I<=n;++I)if(abs(h[I])<i)++gs;
				for(auto cu:v2){
					if(cu<x)++gs;
				}
				v2.emplace_back(x);
				hz[k]=hz[k+1]+gs;
			}
			for(int k=0;k<=A+B;++k){
				if(A1[k]+A2[k+1]!=A)continue;
				if(B1[k]+B2[k+1]!=B)continue;
				f[i][j^(k&1)]=min(f[i][j^(k&1)],f[i+1][j]+qz[k]+hz[k+1]);
			}
		}
		he+=A+B;
	}
	long long ans=min(f[1][0],f[1][1]);
	if(ans>1e18)puts("-1");
	else printf("%lld\n",ans);
	return 0;
}