#include <iostream>
#include<fstream>
#include<algorithm>
#define N 100005
using namespace std;
ifstream fin("heavymetal.in");
ofstream fout("heavymetal.out");

struct pereche
{
    int x,y;
};

pereche a[N];
int lg[N];//lg[i]=durata maxima de spectacole care s ar termina cu spectacolul i
int n;

int compara(int i,int j)//le ordonam crescator dupa timpul de final
{
    if(a[i].y>a[j].y)return 1;
    if(a[i].y==a[j].y&&a[i].x>a[j].x)return 1;//crescator dupa timpul de inceput
    return 0;
}

int pivotare(int s,int d)
{
    int pasi=0,pasj=1,i=s,j=d;
    int p=s+rand()%(d-s+1);
    pereche aux=a[s];a[s]=a[p];a[p]=aux;

    while(i<j)
    {
        if(compara(i,j)==1)
        {
            aux=a[i];a[i]=a[j];a[j]=aux;
            pasi=1-pasi;
            pasj=1-pasj;
        }
        i+=pasi;
        j-=pasj;
    }
    return i;
}

void qs(int s,int d)
{
    if(s<d)
    {
        int p=pivotare(s,d);
        qs(s,p-1);
        qs(p+1,d);
    }
}

void bubblesort()
{
    int i;
    pereche aux;
    bool ordo=false;
    while(ordo=false)
    {
    ordo=true;
    for(i=1;i<n;++i)
        if(compara(i,i+1)==1)
    {
        ordo=false;
        aux=a[i];a[i]=a[i+1];a[i+1]=aux;
    }
    }
}


void solve()
{
    int i,j,lgmax=0,timp;
    for(i=1;i<=n;++i)
    {
        lg[i]=a[i].y-a[i].x;//pp ca e doar el
        timp=lg[i];
        for(j=1;j<i;++j)//incercam sa il punem dupa el
            if(a[j].y<=a[i].x&&lg[j]+timp>lg[i])//daca poate incepe si daca ne da un timp mai bun
        {
            cout<<a[j].y<<" "<<a[i].x<<"\n";
            lg[i]=lg[j]+timp;
            if(lg[i]>lgmax)lgmax=lg[i];//actualizam si maximul
        }
    }
    fout<<lgmax;
    //for(i=1;i<=n;++i)cout<<lg[i]<<" ";

}

void print()
{
    int i;
    for(i=1;i<=n;++i)

        fout<<a[i].x<<" "<<a[i].y<<"\n";
}

int main()

{
    int i;
    fin>>n;
    for(i=1;i<=n;++i)
        fin>>a[i].x>>a[i].y;
    qs(1,n);
    //bubblesort();
   // print();
    solve();


    return 0;
}