#include <iostream>
#include <fstream>
#include <vector>

#define Nmax 100000
#define Mmax 200000

using namespace std;

ifstream finput;
ofstream foutput;

int N, M;
vector <int> adj[Mmax];
vector < vector <int> > sort;
int path[Mmax];
int checked[Nmax];

int search (int);

int main () {
    int num, i, a, b, k, t, found;

    finput.open ("input.txt");
    finput >> N >> M;
    num = 0;
    for (i = 0; i < M; i ++) {
        num ++;
        finput >> a >> b;
        b += Nmax;
        if (num <= N) adj[a].push_back(b);
        else adj[b].push_back(a);
    }
    finput.close ();
    num = 0;
    found = 0;
    while (num < N && !found) {
        found = search (num);
        num ++;
    }
    foutput.open ("output.txt");
    if (!found) foutput << -1;
    else {
        for (i = 0; i < N; i++)
            if (!checked[i]) {
                vector<int> row;
                row.push_back (i);
                row.push_back (adj[i][0]-Nmax);
                sort.push_back (row);
            }
        num = sort.size();
        for (i = 0; i < num - 1; i ++) 
            for (k = 0; k < num - 1 - i; k ++)
                if (sort[k][0] > sort[k+1][0]) {
                    t = sort[k][0];
                    sort[k][0] = sort[k+1][0];
                    sort[k+1][0] = t;
                    t = sort[k][1];
                    sort[k][1] = sort[k+1][1];
                    sort[k+1][1] = t;
                }
        for (i = 0; i < num; i ++)
            foutput << sort[i][0] << ' ' << sort[i][1] << '\n';    
    }
    foutput.close (); 

    return 0;
}

int search (int v) {
    int u, found;

    if (path[v]) {
        if (v < Nmax) return 1;
        else return 0;
    }
    path[v] = 1;
    found = 0;
    for (u = 0; u < adj[v].size (); u++) {
        found = search (adj[v][u]);
        if (found == 1 && v >= Nmax) {
            vector<int> row;
            row.push_back (adj[v][u]);
            row.push_back (v-Nmax);
            sort.push_back (row);
            checked[adj[v][u]] = 1;
        }
        if (found == 1 && v < Nmax && checked[v]) found = 2;
        if (found) {
            path[v] = 0;
            return found;
        }
    }
    path[v] = 0;

    return 0;
}