#include <fstream>
#include <algorithm>
#include <vector>
#include <stack>

using namespace std;

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

int N;
int nodnow, pred, nr_nod;
int muchie[10][10];
vector<int> V[10], A[10][10];
stack<int> ST;
bool instack[10], nr[10], used[50002];

int is_euler(int nod)
{
    ST.push(nod);
    instack[nod] = true;

    while (!ST.empty())
    {
        int now = ST.top();
        ST.pop();
        for (vector<int>::iterator it = V[now].begin(); it != V[now].end(); ++it)
        {
            if (!instack[*it])
            {
                ST.push(*it);
                instack[*it] = true;
            }
        }
    }

    int ok = 1;
    for (int i = 0; i <= 9; ++i)
    {
        if (!nr[i])
            continue;
        if (V[i].size() % 2 == 1 || !instack[i])
        {
            if (V[i].size() % 2 == 1)
            {
                ++nr_nod;
                nodnow = i;
                if (nr_nod == 3)
                {
                    ok = 0;
                    break;
                }
            }
            if (!instack[i])
            {
                ok = 0;
                break;
            }
        }
    }
    nr_nod = 0;

    return ok;
}

void solve_euler(int nod)
{
    ST.push(nod);

    while (!ST.empty())
    {
        int now = ST.top();

        bool ok = true;
        for (vector<int>::iterator it = V[now].begin(); it != V[now].end(); ++it)
        {
            if (!muchie[now][*it])
                continue;
            ok = false;
            ST.push(*it);
            --muchie[now][neighbour];
            --muchie[neighbour][now];
            break;
        }
        if (ok)
        {
            //fout << now << ' ';
            if (!nr_nod)
            {
                pred = now;
                ST.pop();
                nr_nod = 1;
                continue;
            }
            bool ok = false;
            for (vector<int>::iterator it = A[pred][now].begin(); it != A[pred][now].end(); ++it)
            {
                if (!used[*it])
                {
                    ok = true;
                    used[*it] = true;
                    fout << *it << ' ' << 0 << '\n';
                    continue;
                }
            }
            if (!ok)
            {
                for (vector<int>::iterator it = A[now][pred].begin(); it != A[now][pred].end(); ++it)
                {
                    if (!used[*it])
                    {
                        used[*it] = true;
                        fout << *it << ' ' << 1 << '\n';
                        continue;
                    }
                }
            }
            pred = now;
            ST.pop();
        }
    }
}

int main()
{
    fin >> N;
    for (int i = 1, nod1, nod2; i <= N; ++i)
    {
        fin >> nod1 >> nod2;
        nr[nod1] = true;
        nr[nod2] = true;
        nodnow = nod2;
        ++muchie[nod1][nod2];
        ++muchie[nod2][nod1];

        A[nod1][nod2].push_back(i);
        V[nod1].push_back(nod2);
        V[nod2].push_back(nod1);
    }

    if (!is_euler(nodnow))
    {
        fout << 0 << '\n';
        fin.close();
        fout.close();
        return 0;
    }

    fout << 1 << '\n';
    solve_euler(nodnow);

    fin.close();
    fout.close();
    return 0;
}