#include <iostream>
#include <stack>
#include <vector>
#include <fstream>
#define Nmax 100005

using namespace std;

ifstream f("ctc.in");
ofstream g("ctc.out");

int n, m, x, y;
int ctc;
int seen[Nmax];
vector <int> ::iterator it;
vector <int> v1[Nmax], v2[Nmax], ans[Nmax];
stack <int> st;

void dfs1(int x)
{
    seen[x]=1;
    for (int i = 0, l=v1[x].size(); i < l; i++)
    {
        int y=v1[x][i];
        if(seen[y] == 1) continue;
        dfs1(y);
    }
    st.push(x);
}

void dfs2(int x)
{
    seen[x]=-1;
    for (int i = 0, l=v2[x].size(); i < l; i++)
    {
        int y=v2[x][i];
        if(seen[y] == -1) continue;
        dfs2(y);
    }
    ans[ctc].push_back(x);
}

int main()
{
    f >> n >> m;
    for (int i = 1; i <= m; i++)
    {
        f >> x >> y;
        v1[x].push_back(y);
        v2[y].push_back(x);
    }

    for (int i = 1; i <= n; i++)
        if (!seen[i]) dfs1(i);

    while(!st.empty())
    {
        if(seen[st.top()] == -1)
        {
            st.pop();
            continue;
        }
        ctc++;
        dfs2(st.top());
        st.pop();
    }
    g << ctc << '\n';

    for (int i = 1; i <= ctc; i ++)
    {
        for (it=ans[i].begin(); it!=ans[i].end(); it++)
            g << *it << ' ';
        g << '\n';
    }


    return 0;
}