# include <iostream>
# include <cstdio>
# include <queue>
# include <vector>
# include <stack>
# include <map>
# include <cmath>
# include <algorithm>
# include <stdio.h>
using namespace std;
int a[100005][3];
int dp[100005];
int main()
{
freopen ("negsort.out","w",stdout);freopen ("negsort.in","r",stdin);
int n;
scanf("%d",&n);
int i;
scanf("%d",&a[1][0]);
int ans=0;
int f=0;
bool fl1=1,fl2=1;
int bro=0,brp=0;
int j;
for(i=2;i<=n;i++)
{
    scanf("%d",&a[i][0]);
    if(abs(a[i-1][0])>abs(a[i][0]))
    {
        if(a[i-1][1]==1||fl1==0){printf("-1\n");return 0;}
        a[i-1][2]=1;
        if(a[i-1][0]>0){ans++;a[i-1][0]*=(-1);}
        ans+=brp;
        bro=0;
        brp=0;
        fl1=1;
        fl2=1;
        f=0;
    }
    if(abs(a[i-1][0])<abs(a[i][0]))
    {
        if(a[i][2]==1||fl2==0){printf("-1\n");return 0;}
        a[i][1]=1;
        if(a[i][0]<0){ans++;a[i-1][0]*=(-1);}
        if(f!=0)
        {
            brp=0;
            bro=0;
            for(j=f;j<=i;j++)
{
    if(a[j][0]<0)
    {
        if(dp[j-1]+1<brp)
        {
            dp[j]=dp[j-1]+1;
            brp++;
        }
        else
        {
            dp[j]=brp;
            bro++;
        }
    }
    else
        {dp[j]=dp[j-1];brp++;}
    //   cout<<brp<<endl;
}
ans+=dp[j];
        }
        //ans+=bro;

 bro=0;
        brp=0;
        fl1=1;
        fl2=1;
        f=0;
    }
    if(abs(a[i-1][0])==abs(a[i][0]))
    {
        if(f==0)f=i-1;
        if(a[i-1][0]<0)bro++;
        else
            brp++;
        if(a[i-1][1]==1)fl1=0;
        if(a[i-1][2]==1)fl2=0;

    }
  //  cout<<ans<<endl;
}
//cout<<"**"<<ans<<endl;
 if(a[n][0]<0)bro++;
        else
            brp++;
            if(abs(a[n][0])==abs(a[n-1][0])){
        if(a[i-1][1]==1)fl1=0;
        if(a[i-1][2]==1)fl2=0;
if(fl1==0&&fl2==0){printf("-1\n");return 0;}
if(fl1==0)ans+=bro;
else
if(fl2==0)ans+=brp;
else{
        //cout<<1<<endl;
        brp=0;
bro=0;
if(f!=0)
for(i=f;i<=n;i++)
{
    if(a[i][0]<0)
    {
        if(dp[i-1]+1<brp)
        {
            dp[i]=dp[i-1]+1;
            brp++;
        }
        else
        {
            dp[i]=brp;
            bro++;
        }
    }
    else
        {dp[i]=dp[i-1];brp++;}
    //   cout<<brp<<endl;
}
ans+=dp[n];}}
printf("%d\n",ans);

}