#include<fstream>
#include<cstring>
using namespace std;
typedef struct celula{
           int nod;
           celula *next;
           }*lista;
lista graf[205],v;
int cost[205][205],i,j,n,m,x,y,tata[205],coada[205],s,d,sol;
bool ok,viz[205];

void update(){
     int flow=1000,aux=d;
      while (tata[aux]!=aux) { flow=min(flow,cost[tata[aux]][aux]); aux=tata[aux]; }
       aux=d; sol+=flow;
      while (tata[aux]!=aux) { cost[tata[aux]][aux]-=flow; cost[aux][tata[aux]]+=flow; aux=tata[aux]; }
}

void bfs(){
     int begin,end,i; ok=0;
       tata[0]=0; begin=end=1; coada[1]=0;
      while (begin<=end) {
            int nod=coada[begin];
            for (lista p=graf[nod]; p; p=p->next)
             if (cost[nod][p->nod]>0) {
                         tata[p->nod]=nod;
                         if (p->nod==d) { ok=1; update(); }
                             else { ++end; coada[end]=p->nod; }
                  }
            ++begin;
      }
}


void muchie(int x, int y) { v=new celula; v->nod=y; v->next=graf[x]; graf[x]=v; }

int main(void){
    ifstream fin("harta.in");
    ofstream fout("harta.out");
    fin>>n; d=2*n+1; s=0;
    for (i=1; i<=n; ++i) {
        fin>>x>>y; m+=x; cost[s][i]=x; cost[n+i][d]=y; muchie(s,i); muchie(n+i,d);
         for (j=1; j<=n; ++j)
          if (j!=i){ cost[i][n+j]=1; muchie(i,n+j); }
        }
    fout<<m<<"\n"; ok=1;
     while (ok) bfs();
    //  fout<<sol<<"\n";
    for (i=1; i<=n; ++i) 
     for (j=1; j<=n; ++j)
      if (cost[i][n+j]==0&&i!=j) fout<<i<<" "<<j<<"\n";
 return(0);
}