不是我怎么可能错啊啊啊啊啊，是不是SPJ有误

#include<bits/stdc++.h>
#define int long long
using namespace std;
long long sum=0; 
struct node{
    int x,y,id;
}a[5000005];
bool cmp(node xx,node yy)
{
    if(xx.x==yy.x)return xx.y<yy.y;
    else return xx.x<yy.x;
}
signed main()
{
    int n;cin>>n;
    if(n%2==1)
    {
    	cout<<-1;
    	return 0;
	}
    for(int i=1;i<=n;i++)
    {
        cin>>a[i].x>>a[i].y;
        a[i].id=i;
    }
    for(int i=1;i<=n;i+=2)
    		sum+=a[i+1].x-a[i].x;
	cout<<sum<<endl;
	for(int i=1;i<=n;i+=2)
	cout<<a[i].id<<" "<<a[i+1].id<<endl;
    return 0;
}