#include <bits/stdc++.h>

using namespace std;

#define maxn 300000

#define INF 9999999

int n, m, cal[maxn], num[maxn], cur[maxn];

int tot, mark[][], rec[][], lev[maxn];

int S, T, Q[maxn], d[maxn], deg[maxn];

char s1[maxn], s2[maxn];

priority_queue <int, vector <int>, greater <int> > q;

int read()

{

    int x = , k = ;

    char c; c = getchar();

    while(c < '' || c > '') { if(c == '-') k = -; c = getchar(); }

    while(c >= '' && c <= '') x = x *  + c - '', c = getchar();

    return x * k;

}

struct edge

{

    int cnp, to[maxn], last[maxn], head[maxn], f[maxn], F[maxn];

    edge() { cnp = ; }

    void add(int u, int v, int fl)

    {

    //    cout << "*****" << u << " " << v << " " << fl << endl;

        to[cnp] = v, f[cnp] = F[cnp] = fl, last[cnp] = head[u], head[u] = cnp ++;

        to[cnp] = u, f[cnp] = F[cnp] = , last[cnp] = head[v], head[v] = cnp ++;

    }

}E1;

struct node

{

    int u, v;

}id[maxn];

bool bfs()

{

    queue <int> q;

    memset(lev, , sizeof(lev)); lev[S] = ;

    q.push(S);

    while(!q.empty())

    {

        int u = q.front(); q.pop();

        for(int i = E1.head[u]; i; i = E1.last[i])

        {

            int v = E1.to[i];

            if(E1.f[i] && !lev[v])

            {

                lev[v] = lev[u] + ;

                q.push(v);

            }

        }

        if(lev[T]) return ;

    }

    return ;

}

int dfs(int u, int nf)

{

    if(u == T || !nf) return nf;

    int tf = ;

    for(int i = E1.head[u]; i; i = E1.last[i])

    {

        int v = E1.to[i];

        if(!E1.f[i] || lev[v] != lev[u] + ) continue;

        int af = dfs(v, min(E1.f[i], nf));

        tf += af, nf -= af;

        E1.f[i] -= af, E1.f[i ^ ] += af;

    }

    return tf;

}

int dinic()

{

    int nf = ;

    while(bfs()) nf += dfs(S, INF);

    return nf;

}

void dfs2(int u)

{

    for(int i = E1.head[u]; i; i = E1.last[i])

    {

        int v = E1.to[i]; if(!E1.f[i ^ ]) continue;

        if(u > m && u <= tot + m && v >=  && v <= m)

            for(int j = ; j <= E1.f[i ^ ]; j ++)

            {

                int t = u - m; t = (id[t].u == v) ? id[t].v : id[t].u;

                printf("%d %d\n", num[t], cur[v] ++);

            }

        if(u == S) dfs2(v);

    }

}

void Search(int now)

{

    if(now >= m - )

    {

        int t = ;

        for(int i = ; i <= m; i ++) d[i] = deg[i];

        for(int i = ; i <= m; i ++) if(!d[i]) q.push(i);

        memset(mark, , sizeof(mark));

        while(!q.empty() && t <= m - )

        {

            int u = q.top(); q.pop();

            int x = u, y = Q[t]; if(x > y) swap(x, y);

            mark[x][y] = ; d[Q[t]] --;

            if(!d[Q[t]]) q.push(Q[t]); t ++;

        }

        if(q.size() >= )

        {

            int x = q.top(); q.pop(); int y = q.top(); q.pop();

            mark[x][y] = ;

        }else if(q.size() >= ) q.pop();

        for(int i = ; i < E1.cnp; i ++) E1.f[i] = E1.F[i];

        for(int i = E1.head[S]; i; i = E1.last[i])

        {

            int v = E1.to[i]; if(!v) continue; v -= m;

            int x = id[v].u, y = id[v].v;

            if(x > y) swap(x, y);

            E1.f[i] -= mark[x][y];

            if(E1.f[i] < ) return;

        }

        if(dinic() == n - m)

        {

            for(int i = ; i <= m; i ++)

                for(int j = i + ; j <= m; j ++)

                    if(mark[i][j]) printf("%d %d\n", num[i], num[j]);

            for(int i = ; i <= m; i ++) cur[i] ++;

            dfs2(S);

            exit();

        }

        return;

    }

    for(int i = ; i <= m; i ++)

        deg[i] ++, Q[now] = i, Search(now + ), deg[i] --;

}

int main()

{

    n = read(); int t = n;

    while(t) { m ++; t /= ; }

    for(int i = , l = ; i <= m; l *= , i ++) num[i] = cur[i] = l;

    for(int i = , l = ; i < m; l *= , i ++) cal[i] = l *  - num[i];

    cal[m] = n - num[m] + ; S = , T = m * m + m + ;

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

    {

        scanf("%s%s", s1 + , s2 + );

        int l1 = strlen(s1 + ), l2 = strlen(s2 + );

        if(l1 > l2) swap(l1, l2); rec[l1][l2] ++;

    }

    for(int i = ; i <= m; i ++)

        for(int j = i; j <= m; j ++)

        {

            id[++ tot].u = i, id[tot].v = j;

            E1.add(S, tot + m, rec[i][j]);

            E1.add(tot + m, i, INF); E1.add(tot + m, j, INF);

        }

    for(int i = ; i <= m; i ++) E1.add(i, T, cal[i] - );

    Search();

    printf("-1\n");

    return ;

}