#include<fstream>
#include<vector>
#include<queue>

using namespace std;

ifstream fin( "harta.in" ); ofstream fout( "harta.out" );

typedef vector< int > graf;

const int nmax = 2 + 2 * 100;
int S, D;
int t[ nmax + 1 ];
int f[ nmax + 1 ][ nmax + 1 ], c[ nmax + 1 ][ nmax + 1 ];
graf g[ nmax + 1 ];

inline int min2( int a, int b ) {
    return ( a < b ? a : b );
}
bool bfs() {
    queue< int > q;
    for( int i = S; i <= D; ++ i ) {
        t[ i ] = -1;
    }

    q.push( S );
    t[ S ] = 0;
    while ( !q.empty() ) {
        int x = q.front();
        q.pop();

        for( graf::iterator it = g[ x ].begin(); it != g[ x ].end(); ++ it ) {
            if ( t[ *it ] == -1 && f[ x ][ *it ] < c[ x ][ *it ] ) {
                t[ *it ] = x;
                q.push( *it );
            }
        }
    }

    return ( t[ D ] != -1 );
}
int main() {
    int n, ans;
    fin >> n;

    S = 1; D = 2 * n + 2;
    ans = 0;
    for( int i = 1; i <= n; ++ i ) {
        int x, y;
        fin >> x >> y;
        c[ S ][ i + 1 ] = x;
        g[ S ].push_back( i + 1 );
        g[ i + 1 ].push_back( S );

        c[ i + n + 1 ][ D ] = y;
        g[ i + n + 1 ].push_back( D );
        g[ D ].push_back( i + n + 1 );
        ans += x;
    }
    for( int i = 1; i <= n; ++ i ) {
        for( int j = n + 1; j <= n + n; ++ j ) {
            if ( i != j - n ) {
                g[ i + 1 ].push_back( j + 1 );
                g[ j + 1 ].push_back( i + 1 );
                c[ i + 1 ][ j + 1 ] = 1;
            }
        }
    }

    while ( bfs() ) {
        for( graf::iterator it = g[ D ].begin(); it != g[ D ].end(); ++ it ) {
            if ( f[ *it ][ D ] < c[ *it ][ D ] && t[ *it ] != -1 ) {
                int val = c[ *it ][ D ] - f[ *it ][ D ];
                for( int nod = *it; nod != S; nod = t[ nod ] ) {
                    val = min2( val, c[ t[ nod ] ][ nod ] - f[ t[ nod ] ][ nod ] );
                }

                f[ *it ][ D ] += val;
                f[ D ][ *it ] -= val;
                for( int nod = *it; nod != S; nod = t[ nod ] ) {
                    f[ t[ nod ] ][ nod ] += val;
                    f[ nod ][ t[ nod ] ] -= val;
                }
            }
        }
    }

    fout << ans << "\n";
    for( int i = 1; i <= n; ++ i ) {
        for( int j = 1; j <= n; ++ j ) {
            if ( f[ i + 1 ][ j + n + 1 ] == 1 ) {
                fout << i << " " << j << "\n";
            }
        }
    }
    fin.close();
    fout.close();
    return 0;
}