#include<cstdio>

#include<queue>

#include<cstring>

using namespace std;

const int MAXN = 1e5 + , INF = 1e9 + ;

inline int read() {

    char c = getchar(); int x = , f = ;

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

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

    return x * f;

}

int N, M;

vector<int> v[MAXN];

int link[MAXN], vis[MAXN], cnt = ;

bool Arg(int x) {

    for(int i = ; i < v[x].size(); i++) {

        int to = v[x][i];

        if(vis[to] == cnt) continue; vis[to] = cnt;

        if(!link[to] || Arg(link[to]))

            {link[to] = x; link[x] = to; return ;}

    }

    return ;

}

int Hunary() {

    int ans = ;

    for(int i = ; i <= N; i++, cnt++)

        if(Arg(i))

            ans++;

    return ans;

}

int main() {

    N = read(); M = read();

    for(int i = ; i <= M; i++) {

        int x = read(), y = read();

        v[x].push_back(y + N);

    }

    int ans = N - Hunary();

    memset(vis, , sizeof(vis));

    for(int i = ; i <= N; i++) {

        int x = i + N;

        if(vis[i]) continue;

        do

            printf("%d ", x = x - N);

        while(vis[x] = , x = link[x]);

        puts("");

    }

    printf("%d", ans);

    return ;

}