#include<stdio.h>#include<iostream>#include<algorithm>#include<cmath>#define pi acos(-1.0)#define N 100010#define r 6370#define eps 1e-8#define inf 0xfffffffusing namespace std;struct Point{ int x,y; int id;};struct Line{ int x,y1,y2; Line(){} Line(int x0,int y11,int y22):x(x0),y1(y11),y2(y22){}};Line l[N];Point p[N];int con[N][2];int n;int ln;int cmp_x(Point a,Point b){ if(a.x==b.x) return a.y<b.y; return a.x<b.x;}int cmp_y(Point a,Point b){ if(a.y==b.y) return a.x<b.x; return a.y<b.y;}int Judge(Point a,Point b){ int y=a.y,x1=a.x,x2=b.x; for(int i=0;i<ln;i++) { if(x1<l[i].x && x2>l[i].x && l[i].y1<y && l[i].y2>y) return 1; } return 0;}int main(){ int t; scanf("%d",&t); while(t--) { scanf("%d",&n); for(int i=0;i<n;i++) { scanf("%d%d",&p[i].x,&p[i].y); p[i].id=i; } int sum=0; sort(p,p+n,cmp_x); int cnt=1; int flag=0; ln=0; for(int i=1;i<n&&!flag;i++) { if(p[i].x!=p[i-1].x) { if(cnt&1) flag=1; cnt=1; } else { cnt++; if((cnt&1)==0) { sum+=p[i].y-p[i-1].y; con[p[i].id][0]=p[i-1].id;//前驱 con[p[i-1].id][0]=p[i].id;//后继 l[ln++]=Line(p[i].x,p[i-1].y,p[i].y); } } } sort(p,p+n,cmp_y); cnt=1; for(int i=1;i<n && !flag;i++) { if(p[i].y!=p[i-1].y) { if(cnt&1) flag=1; cnt=1; } else { cnt++; if((cnt&1)==0) { sum+=p[i].x-p[i-1].x; con[p[i].id][1]=p[i-1].id;//前驱 con[p[i-1].id][1]=p[i].id;//后继 if(Judge(p[i-1],p[i])) flag=1; } } } int pp=1,x=0,cc=0; do { x=con[x][pp]; pp=1-pp; cc++; }while(x!=0 && !flag); if(cc!=n) flag=1; if(!flag) cout<<sum<<endl; else cout<<-1<<endl; } return 0;}
