#include<bits/stdc++.h>
using namespace std;
struct star{
    long long index,x;
}a[500005];
long long n,y,ans=0;
bool cmp(star a,star b){ return a.x<b.x; }
int main(){
    ios::sync_with_stdio(false);
    cin.tie(0);
    cout.tie(0);
    cin>>n;
    if(n%2==1){
        cout<<-1;
        return 0;
    }
    for(long long i=1;i<=n;i++){
        cin>>a[i].x>>y;
        a[i].index=i;   
    }
    sort(a+1,a+n+1,cmp);
    for(long long i=1;i<=n/2;i++) ans+=a[i*2].x-a[i*2-1].x;
    cout<<ans<<'\n';
    for(long long i=1;i<=n/2;i++) cout<<a[i*2-1].index<<' '<<a[i*2].index<<'\n';
    return 0;
}

$AC\ 3$ 个点其余全 $WA$，报 Wrong Answer.wrong answer The segments overlop.