#include <bits/stdc++.h>
using namespace std;

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

int n, m, in[256];
vector <int> g[256];

struct edge {
    int x, y;
};

vector <edge> add;
vector <int> r;

int main() {

    fin >> n >> m;

    for (int i = 1; i <= m; i++)
    {
        int x, y;
        fin >> x >> y;
        g[x].push_back(y);
        in[y]++;
    }

    vector <int> A, B;

    for (int i = 1; i <= n; i++)
        if (in[i] == 0)
            A.push_back(i);

    while (A.size())
    {
        B.clear();

        r.push_back(A[0]);

        for (auto& i : g[A[0]])
            if (in[i] == 1)
                B.push_back(i), in[i] = 0;
            else
                in[i]--;

        for (int i = 1; i < A.size(); i++)
        {
            add.push_back({ A[i - 1], A[i] }), r.push_back(A[i]);

            for (auto& i : g[A[i]])
                if (in[i] == 1)
                    B.push_back(i), in[i] = 0;
                else
                    in[i]--;
        }

        swap(A, B);
    }

    fout << add.size() << '\n';

    for (auto& i : add)
        fout << i.x << ' ' << i.y << '\n';

    for (auto& i : r)
        fout << i << ' ';
    
    return 0;

}