# include <algorithm>
# include <cstdio>
# include <cstring>
# include <vector>
using namespace std;

# define x first
# define y second

const char *FIN = "strazi.in", *FOU = "strazi.out";
const int MAX = 260;

vector <int> G[MAX];
pair <int, int> dp[MAX];
int N, M, E, sol[MAX], st[MAX], dr[MAX], viz[MAX];

bool dfs (int S) {
    if (viz[S]) return 0;
    else viz[S] = 1;
    for (vector <int> :: iterator it = G[S].begin (); it != G[S].end (); ++it)
        if (st[*it] == 0 || dfs (st[*it])) {
            st[*it] = S, dr[S] = *it;
            return 1;
        }
    return 0;
}

int main (void) {
    freopen (FIN, "r", stdin);
    freopen (FOU, "w", stdout);

    scanf ("%d %d", &N, &M);
    for (int i = 1, x, y; i <= M; ++i) {
        scanf ("%d %d", &x, &y);
        G[x].push_back (y);
    }
    for (int solx = 1; solx;) {
        solx = 0, memset (viz, 0, sizeof (viz));
        for (int i = 1; i <= N; ++i)
            if (dr[i] == 0) solx |= dfs (i);
    }
    for (int i = 1, j = 0; i <= N; ++i)
         if (st[i] == 0) {
             dp[++dp[0].x] = make_pair (j, i);
             sol[++sol[0]] = i;
             for (j = i; dr[j]; j = dr[j])
                 sol[++sol[0]] = dr[j];
         }
    printf ("%d\n", dp[0].x - 1);
    for (int i = 2; i <= dp[0].x; ++i)
        printf ("%d %d\n", dp[i].x, dp[i].y);
    for (int i = 1; i <= sol[0]; ++i)
        printf ("%d ", sol[i]);
}