#include<iostream>

#include<cstdio>

#include<cstring>

#include<cmath>

#include<algorithm>

using namespace std;

#define rep0(i,l,r) for(int i = (l);i < (r);i++)

#define rep1(i,l,r) for(int i = (l);i <= (r);i++)

#define rep_0(i,r,l) for(int i = (r);i > (l);i--)

#define rep_1(i,r,l) for(int i = (r);i >= (l);i--)

#define inf 0x7fffffff

#define pow(a) (a)*(a)

typedef long long ll;

template<typename T>

void read1(T &m)

{

    T x=,f=;char ch=getchar();

    while(ch<''||ch>''){if(ch=='-')f=-;ch=getchar();}

    while(ch>=''&&ch<=''){x=x*+ch-'';ch=getchar();}

    m = x*f;

}

template<typename T>

void read2(T &a,T &b){read1(a);read1(b);}

template<typename T>

void read3(T &a,T &b,T &c){read1(a);read1(b);read1(c);}

typedef pair<int,int> PII;

#define A first

#define B second

#define MK make_pair

const int MAXN = <<;

int d[MAXN],stk[MAXN],val[MAXN];

PII v[MAXN];

int main()

{

    int p = ,n;

    read1(n);

    n <<= ;

    for(int i = ;i < n;i += ){

        read2(v[i].A,v[i+].A);

        if(v[i].A > v[i+].A) swap(v[i].A,v[i+].A);

        v[i].B = i;v[i+].B = i+;

    }

    sort(v,v+n);

    ll ans  = ;

    rep0(i,,n){

        if((v[i].B&) == ) stk[++p] = v[i].B,val[p] = v[i].A;

        else{

            if(v[i].B- == stk[p]){

                p--;

                while(p && d[stk[p]]) p--;

            }

            if(!p) ans += v[i].A - val[];

            else d[v[i].B^] = ;

        }

    }

    printf("%lld\n",ans);

    return ;

}