#include <bits/stdc++.h>

using namespace std;

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

const int nmax = 1e5+5;
vector<int>mch[nmax],mch_rev[nmax];
int n,m,a,b;
bool vis[nmax],v_rev[nmax];
stack<int>st;
vector<int>cr_comp;
vector<vector<int>>anses;

void dfs(int nod)
{
    vis[nod]=true;
    for(auto it:mch[nod])
        if(!vis[it])
            dfs(it);
    st.push(nod);
}

void dfs_rev(int nod)
{
    v_rev[nod]=true;
    cr_comp.push_back(nod);
    for(auto it:mch_rev[nod])
        if(!v_rev[it])
            dfs_rev(it);
}


int main()
{
    fin >> n >> m;
    for(int i=1 ; i<=m ;++i)
    {
        fin >> a >> b;
        mch[a].push_back(b);
        mch_rev[b].push_back(a);
    }
    for(int i=1 ; i<=n ;++i)
        if(!vis[i])
            dfs(i);

    while(!st.empty())
    {
        int crt = st.top();
        if(!v_rev[crt])
        {
            dfs_rev(crt);
            anses.push_back(cr_comp);
            cr_comp.clear();
        }
        st.pop();
    }
    fout << anses.size() << '\n';
    for(auto comp:anses)
    {
        for(auto it:comp)
            fout << it << ' ';
        fout << '\n';
    }
    return 0;
}