Problem:
Score : 500 points

Problem Statement

There are N towns on a plane. The i-th town is located at the coordinates (x_i,y_i). There may be more than one town at the same coordinates.

You can build a road between two towns at coordinates (a,b) and (c,d) for a cost of min(|a-c|,|b-d|) yen (the currency of Japan). It is not possible to build other types of roads.

Your objective is to build roads so that it will be possible to travel between every pair of towns by traversing roads. At least how much money is necessary to achieve this?

Constraints

2 ≤ N ≤ 10^5

0 ≤ x_i,y_i ≤ 10^9

All input values are integers.

Input

Input is given from Standard Input in the following format:

N
x_1 y_1
x_2 y_2
:
x_N y_N

Output

Print the minimum necessary amount of money in order to build roads so that it will be possible to travel between every pair of towns by traversing roads.

Sample Input 1

3
1 5
3 9
7 8

Sample Output 1

3

Build a road between Towns 1 and 2, and another between Towns 2 and 3. The total cost is 2+1=3 yen.

Sample Input 2

6
8 3
4 9
12 19
18 1
13 5
7 6

Sample Output 2

8

Solution in C (GCC 5.4.1) (judge verdict: Accepted)

#include<stdio.h>
#include<stdlib.h>
#include<string.h>


typedef struct pairingHeapNode{
  struct pairingHeapNode *next;
  struct pairingHeapNode *child;
  unsigned long long int val[];
} heapNode;

typedef struct pairingHeap{
  heapNode *root;
  int heapSize;
  size_t size;
  int (*cmp)(const void *,const void *);
} heap;

heapNode* newHeapNode(const void *v,const size_t size){
  heapNode *res=(heapNode *)malloc(sizeof(heapNode)+size);
  memcpy(res->val,v,size);
  res->next=NULL;
  res->child=NULL;
  return res;
}

void freeAllNode(heapNode *t){
  if(t==NULL) return;
  freeAllNode(t->next);
  freeAllNode(t->child);
  free(t);
  return;
}

heap* newHeap(const size_t size,int (*cmp)(const void *,const void *)){
  heap *res=(heap *)malloc(sizeof(heap));
  res->root=NULL;
  res->heapSize=0;
  res->size=size;
  res->cmp=cmp;
  return res;
}

void freeHeap(heap *h){
  freeAllNode(h->root);
  free(h);
  return;
}

int getSize(const heap *h){
  return h->heapSize;
}

int isEmpty(const heap *h){
  return getSize(h)==0;
}

heapNode* meld(heapNode *a,heapNode *b,int (*cmp)(const void *a,const void *b)){
  if(a==NULL) return b;
  if(b==NULL) return a;
  if(cmp(a->val,b->val)<=0){
    b->next=a->child;
    a->child=b;
    return a;
  } else {
    a->next=b->child;
    b->child=a;
    return b;
  }
}

void push(heap *h,const void *v){
  heapNode *p=newHeapNode(v,h->size);
  h->heapSize++;
  h->root=meld(h->root,p,h->cmp);
  return;
}

void pop(heap *h,void *v){
  if(v!=NULL) memcpy(v,h->root->val,h->size);
  heapNode *lst=h->root->child;
  int (*cmp)(const void *a,const void *b)=h->cmp;
  free(h->root);
  h->heapSize--;
  heapNode *r=NULL;
  while(lst!=NULL && lst->next!=NULL){
    heapNode *a=lst;
    heapNode *b=lst->next;
    heapNode *next=lst->next->next;
    a->next=b->next=NULL;
    r=meld(r,meld(a,b,cmp),cmp);
    lst=next;
  }
  if(lst!=NULL) r=meld(r,lst,cmp);
  h->root=r;
  return;
}

void top(const heap *h,void *v){
  memcpy(v,h->root->val,h->size);
  return;
}

typedef long long int int64;

typedef struct edge{
  int a,b;
  int c;
} edge;

typedef struct indexNode{
  int index;
  int val;
} node;

int cmpNode(const void *a,const void *b){
  return ((node *)a)->val-((node *)b)->val;
}

int cmpEdge(const void *a,const void *b){
  return ((edge *)a)->c-((edge *)b)->c;
}

int root(int *u,int x){
  if(u[x]==x) return x;
  return u[x]=root(u,u[x]);
}

int same(int *u,int x,int y){
  return root(u,x)==root(u,y);
}

void unite(int *u,int x,int y){
  x=root(u,x);
  y=root(u,y);
  if(x==y) return;
  u[x]=y;
}

void run(void){
  int n;
  scanf("%d",&n);
  node *x=(node *)calloc(n,sizeof(node));
  node *y=(node *)calloc(n,sizeof(node));
  int i;
  for(i=0;i<n;i++){
    int a,b;
    scanf("%d%d",&a,&b);
    x[i]=(node){i,a};
    y[i]=(node){i,b};
  }
  qsort(x,n,sizeof(node),cmpNode);
  qsort(y,n,sizeof(node),cmpNode);
  heap *h=newHeap(sizeof(edge),cmpEdge);
  for(i=0;i<n-1;i++){
    push(h,&((edge){x[i].index,x[i+1].index,x[i+1].val-x[i].val}));
    push(h,&((edge){y[i].index,y[i+1].index,y[i+1].val-y[i].val}));
  }
  int cnt=0;
  int *u=(int *)calloc(n,sizeof(int));
  for(i=0;i<n;i++) u[i]=i;
  int64 ans=0;
  for(i=0;cnt<n-1;i++){
    edge e;
    pop(h,&e);
    if(same(u,e.a,e.b)) continue;
    unite(u,e.a,e.b);
    ans+=e.c;
    cnt++;
  }
  printf("%lld\n",ans);
}

int main(void){
  run();
  return 0;
}