#include <bits/stdc++.h>

class kin{
public:
	inline void open(FILE *,int);
	inline void close(void);
	inline void scan(void);
	inline kin &operator>(char &);
	inline kin &operator>(int &);
	inline kin &operator>(long long &);
	inline kin &operator>(double &);
	inline kin &operator>(long double &);
	inline kin &operator>(char *);
	template<class T>
	inline void get(T *,int);
private:
	FILE *fp;
	char *buf;
	int siz;
	int idx;
}in;

class kout{
public:
	inline void open(FILE *,int);
	inline void close(void);
	inline void print(void);
	inline kout &operator<(char);
	inline kout &operator<(int);
	inline kout &operator<(long long);
	inline kout &operator<(double);
	inline kout &operator<(long double);
	inline kout &operator<(const char *);
	template<class T>
	inline void put(T *,int,char,char);
private:
	FILE *fp;
	char *buf;
	int siz;
	int idx;
}out;

template<class E>
class edgeset{
public:
	inline void open(int,int);
	inline void close(void);
	inline int first(int);
	inline int next(int);
	inline void add(int,E);
	inline E &operator[](int);
	inline int vsize(void);
	inline int esize(void);
	inline edgeset();
	inline edgeset(int,int);
private:
	int sizv;
	int size;
	int *idxf;
	int *idxn;
	E *dat;
};

class unionfind{
public:
	inline void open(int);
	inline void close(void);
	inline void unite(int,int);
	inline int same(int,int);
	inline int size(int);
	inline int group(void);
	inline unionfind();
	inline unionfind(int);
private:
	int siz;
	int *par;
	int grp;
	inline int find(int);
};

template<class E>
inline long long kruscal(edgeset<E> &graph){
	int e=graph.esize();
	E *t=new E[e];
	for(int i=0;i<e;++i) t[i]=graph[i];
	std::sort(t,t+e,[](E &x,E &y){return x.wgt<y.wgt;});
	unionfind s(graph.vsize());
	long long ret=0LL;
	for(int i=0;i<e;++i){
		if(!s.same(t[i].start,t[i].end)){
			ret+=t[i].wgt;
			s.unite(t[i].start,t[i].end);
		}
		if(s.group()==1) break;
	}
	delete[] t;
	s.close();
	return ret;
}

int main(int argc,char **argv){
	in.open(stdin,512);
	out.open(stdout,512);
	in.scan();
	int n;
	in>n;
	struct point{
		int cx;
		int cy;
		int num;
	};
	point d[100000];
	for(int i=0;i<n;++i){
		in>d[i].cx>d[i].cy;
		d[i].num=i;
	}
	struct dse{
		int start;
		int end;
		long long wgt;
	};
	int m=n-1;
	edgeset<dse> g(n,m*2);
	std::sort(d,d+n,[](point &p,point &q){return p.cx<q.cx;});
	for(int i=0;i<m;++i) g.add(d[i].num,(dse){d[i].num,d[i+1].num,(long long)std::abs(d[i+1].cx-d[i].cx)});
	std::sort(d,d+n,[](point &p,point &q){return p.cy<q.cy;});
	for(int i=0;i<m;++i) g.add(d[i].num,(dse){d[i].num,d[i+1].num,(long long)std::abs(d[i+1].cy-d[i].cy)});
	out<kruscal(g)<'\n';
	out.print();
	in.close();
	out.close();
	return 0;
}

template<class E>
inline void edgeset<E>::open(int sizva,int sizea){
	sizv=sizva;
	size=0;
	idxf=new int[sizva];
	for(int i=0;i<sizva;++i) idxf[i]=-1;
	idxn=new int[sizea];
	for(int i=0;i<sizea;++i) idxn[i]=-1;
	dat=new E[sizea];
	return;
}
template<class E>
inline void edgeset<E>::close(void){
	sizv=size=0;
	delete[] idxf;
	delete[] idxn;
	idxf=idxn=nullptr;
	delete[] dat;
	dat=nullptr;
	return;
}
template<class E>
inline int edgeset<E>::first(int num){
	return idxf[num];
}
template<class E>
inline int edgeset<E>::next(int idx){
	return idxn[idx];
}
template<class E>
inline void edgeset<E>::add(int num,E val){
	dat[size]=val;
	idxn[size]=idxf[num];
	idxf[num]=size++;
	return;
}
template<class E>
inline E &edgeset<E>::operator[](int idx){
	return dat[idx];
}
template<class E>
inline int edgeset<E>::vsize(void){
	return sizv;
}
template<class E>
inline int edgeset<E>::esize(void){
	return size;
}
template<class E>
inline edgeset<E>::edgeset(){
	sizv=size=0;
	idxf=idxn=nullptr;
	dat=nullptr;
}
template<class E>
inline edgeset<E>::edgeset(int vertex,int siza){
	open(vertex,siza);
}

inline void unionfind::open(int siza){
	siz=siza;
	par=new int[siz];
	for(int i=0;i<siz;++i) par[i]=-1;
	grp=siz;
	return;
}
inline void unionfind::close(void){
	siz=grp=0;
	delete[] par;
	par=nullptr;
}
inline void unionfind::unite(int ndx,int ndy){
	ndx=find(ndx);
	ndy=find(ndy);
	if(ndx==ndy) return;
	if(par[ndx]>par[ndy]){
		par[ndy]+=par[ndx];
		par[ndx]=ndy;
	}
	else{
		par[ndx]+=par[ndy];
		par[ndy]=ndx;
	}
	--grp;
	return;
}
inline int unionfind::same(int ndx,int ndy){
	return find(ndx)==find(ndy)?1:0;
}
inline int unionfind::size(int nd){
	return -par[find(nd)];
}
inline int unionfind::group(void){
	return grp;
}
inline int unionfind::find(int nd){
	if(par[nd]<0) return nd;
	return par[nd]=find(par[nd]);
}
inline unionfind::unionfind(void){
	siz=grp=0;
	par=nullptr;
}
inline unionfind::unionfind(int siza){
	open(siza);
}

inline void kin::open(FILE *fpa,int siza){
	fp=fpa;
	buf=new char[siza];
	siz=siza;
	idx=0;
	return;
}
inline void kin::close(void){
	fp=nullptr;
	delete[] buf;
	buf=nullptr;
	siz=0;
	idx=0;
	return;
}
inline void kin::scan(void){
	int readsiz=(int)std::fread((void *)buf,(std::size_t)1,(std::size_t)siz,fp);
	if(readsiz!=siz) buf[readsiz]='\x00';
	idx=0;
	return;
}
inline kin &kin::operator>(char &var){
	if(!buf[idx]){
		var='\x00';
		return *this;
	}
	var=buf[idx];
	if(++idx==siz) scan();
	if(++idx==siz) scan();
	return *this;
}
inline kin &kin::operator>(int &var){
	if(!buf[idx]){
		var=0;
		return *this;
	}
	int sign=-1;
	if(buf[idx]=='-'){
		sign=1;
		if(++idx==siz) scan();
	}
	var=0;
	while(buf[idx]>='0'){
		var=var*10-(int)(buf[idx]-'0');
		if(++idx==siz) scan();
	}
	var*=sign;
	if(++idx==siz) scan();
	return *this;
}
inline kin &kin::operator>(long long &var){
	if(!buf[idx]){
		var=0LL;
		return *this;
	}
	long long sign=-1LL;
	if(buf[idx]=='-'){
		sign=1LL;
		if(++idx==siz) scan();
	}
	var=0LL;
	while(buf[idx]>='0'){
		var=var*10LL-(long long)(buf[idx]-'0');
		if(++idx==siz) scan();
	}
	var*=sign;
	if(++idx==siz) scan();
	return *this;
}
inline kin &kin::operator>(double &var){
	if(!buf[idx]){
		var=0.0;
		return *this;
	}
	double sign=-1.0;
	if(buf[idx]=='-'){
		sign=1.0;
		if(++idx==siz) scan();
	}
	var=0.0;
	while(buf[idx]>='0'){
		var=var*10.0-(double)(buf[idx]-'0');
		if(++idx==siz) scan();
	}
	if(buf[idx]=='.'){
		if(++idx==siz) scan();
		double dig=1.0;
		while(buf[idx]>='0'){
			var-=(double)(buf[idx]-'0')*(dig/=10.0);
			if(++idx==siz) scan();
		}
	}
	var*=sign;
	if(++idx==siz) scan();
	return *this;
}
inline kin &kin::operator>(long double &var){
	if(!buf[idx]){
		var=0.0L;
		return *this;
	}
	long double sign=-1.0L;
	if(buf[idx]=='-'){
		sign=1.0L;
		if(++idx==siz) scan();
	}
	var=0.0L;
	while(buf[idx]>='0'){
		var=var*10.0L-(long double)(buf[idx]-'0');
		if(++idx==siz) scan();
	}
	if(buf[idx]=='.'){
		if(++idx==siz) scan();
		long double dig=1.0L;
		while(buf[idx]>='0'){
			var-=(long double)(buf[idx]-'0')*(dig/=10.0L);
			if(++idx==siz) scan();
		}
	}
	var*=sign;
	if(++idx==siz) scan();
	return *this;
}
inline kin &kin::operator>(char *var){
	if(!buf[idx]){
		var[0]='\x00';
		return *this;
	}
	int ptr=0;
	while(buf[idx]>='!'){
		var[ptr++]=buf[idx];
		if(++idx==siz) scan();
	}
	var[ptr]='\x00';
	if(++idx==siz) scan();
	return *this;
}
template<class T>
inline void kin::get(T *var,int num){
	for(int i=0;i<num;++i) (*this)>var[i];
	return;
}

inline void kout::open(FILE *fpa,int siza){
	fp=fpa;
	buf=new char[siza];
	siz=siza;
	idx=0;
	return;
}
inline void kout::close(void){
	fp=nullptr;
	delete[] buf;
	buf=nullptr;
	siz=0;
	idx=0;
	return;
}
inline void kout::print(void){
	std::fwrite((void *)buf,(std::size_t)1,(std::size_t)idx,fp);
	idx=0;
	return;
}
inline kout &kout::operator<(char val){
	buf[idx]=val;
	if(++idx==siz) print();
	return *this;
}
inline kout &kout::operator<(int val){
	if(val<0){
		buf[idx]='-';
		if(++idx==siz) print();
	}
	else val*=-1;
	char dig[10];
	int ptr=0;
	do{
		int tmp=val/10;
		dig[ptr++]=(char)-(val-tmp*10)+'0';
		val=tmp;
	}while(val);
	while(ptr--){
		buf[idx]=dig[ptr];
		if(++idx==siz) print();
	}
	return *this;
}
inline kout &kout::operator<(long long val){
	if(val<0LL){
		buf[idx]='-';
		if(++idx==siz) print();
	}
	else val*=-1LL;
	char dig[19];
	int ptr=0;
	do{
		long long tmp=val/10LL;
		dig[ptr++]=(char)-(val-tmp*10LL)+'0';
		val=tmp;
	}while(val);
	while(ptr--){
		buf[idx]=dig[ptr];
		if(++idx==siz) print();
	}
	return *this;
}
inline kout &kout::operator<(double val){
	if(val<0.0){
		buf[idx]='-';
		if(++idx==siz) print();
	}
	else val*=-1.0;
	double dig=1.0;
	while(val/dig<=-10.0) dig*=10.0;
	int tmp;
	while(dig>=1.0){
		buf[idx]=(char)-(tmp=(int)(val/dig))+'0';
		if(++idx==siz) print();
		val-=(double)tmp*dig;
		dig/=10.0;
	}
	buf[idx]='.';
	if(++idx==siz) print();
	for(int i=0;i<12;++i){
		buf[idx]=(char)-(tmp=(int)(val/dig))+'0';
		if(++idx==siz) print();
		val-=(double)tmp*dig;
		dig/=10.0;
	}
	return *this;
}
inline kout &kout::operator<(long double val){
	if(val<0.0L){
		buf[idx]='-';
		if(++idx==siz) print();
	}
	else val*=-1.0L;
	long double dig=1.0L;
	while(val/dig<=-10.0L) dig*=10.0L;
	int tmp;
	while(dig>=1.0L){
		buf[idx]=(char)-(tmp=(int)(val/dig))+'0';
		if(++idx==siz) print();
		val-=(long double)tmp*dig;
		dig/=10.0L;
	}
	buf[idx]='.';
	if(++idx==siz) print();
	for(int i=0;i<16;++i){
		buf[idx]=(char)-(tmp=(int)(val/dig))+'0';
		if(++idx==siz) print();
		val-=(long double)tmp*dig;
		dig/=10.0L;
	}
	return *this;
}
inline kout &kout::operator<(const char *val){
	for(int i=0;val[i];++i){
		buf[idx]=val[i];
		if(++idx==siz) print();
	}
	return *this;
}
template<class T>
inline void kout::put(T *val,int num,char dlm,char end){
	--num;
	for(int i=0;i<num;++i) (*this)<val[i]<dlm;
	(*this)<val[num]<end;
	return;
}


Measured memory_bytes: 9216