sgu 128

#include<cstdio>
#include<iostream>
#include<algorithm>
using namespace std;
const int MAX=10005;

class BIT
{
public:
int a[MAX<<1];

void insert(int pos,int x)
{
while(pos<MAX*2)
{
a[pos]+=x;
pos+=pos&(-pos);
}
}

int query(int pos)
{
int ans=0;
while(pos)
{
ans+=a[pos];
pos-=pos&(-pos);
}
return ans;
}
};

struct point
{
int x,y;
};

BIT bit;
point p[MAX];
int n,s[MAX],pos[MAX],up[MAX],L[MAX];

int find(int x)
{
if(s[x]!=x) s[x]=find(s[x]);
return s[x];
}

void Union(int x,int y)
{
x=find(x);
y=find(y);
if(x!=y) s[x]=y;
}

int cmpx(int a,int b)
{
if(p[a].x!=p[b].x) return p[a].x<p[b].x;
return p[a].y<p[b].y;
}

int cmpy(int a,int b)
{
if(p[a].y!=p[b].y) return p[a].y<p[b].y;
return p[a].x<p[b].x;
}

int deal()
{
int ans=0,i,j,k,t;
for(int i=0;i<n;i++)s[i]=i;
sort(pos,pos+n,cmpx);
for(i=0;i<n;i+=2)
{
j=pos[i];
k=pos[i+1];
if(p[j].x!=p[k].x) return 0;
ans+=p[k].y-p[j].y;
up[j]=k;
Union(j,k);
}
sort(pos,pos+n,cmpy);
for(i=0;i<n;i+=2)
{
j=pos[i];
k=pos[i+1];
if(p[j].y!=p[k].y) return 0;
ans+=p[k].x-p[j].x;
L[j]=1;
Union(j,k);
}
k=find(0);
for(i=1;i<=n-1;i++) if(find(i)!=k) return 0;
sort(pos,pos+n,cmpx);
for(int i=0;i<n;i++)
{
j=pos[i];
k=p[up[j]].y;
t=p[j].y;
if(up[j]&&bit.query(k+MAX)-bit.query(t+MAX+1)) return 0;
if(L[j]) bit.insert(t+MAX+1,1);
else bit.insert(t+MAX+1,-1);
}
return ans;
}

int main()
{
scanf("%d",&n);
int i;
for(int i=0;i<n;i++)scanf("%d%d",&p[i].x,&p[i].y),pos[i]=i;
printf("%d\n",deal());
return 0;
}