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

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

int n, m, global_idx;
vector<vector<int>> adj_list, ans;
vector<int> cc, idx, lowlink, visited, in_stack;

stack<int> S;

void read()
{
    fin>>n>>m;

    adj_list.assign(n+1, vector<int>());
    idx.assign(n+1, -1);
    lowlink.assign(n+1, 0);
    in_stack.assign(n+1, 0);

    for(int i=0; i<m; i++)
    {
        int x, y;
        fin>>x>>y;
        adj_list[x].push_back(y);
    }
}

void dfs(int x)
{
    idx[x] = lowlink[x] = global_idx++;

    S.push(x);
    in_stack[x] = 1;

    for(auto &next:adj_list[x])
    {
        if(idx[next] == -1)
        {
            dfs(next);
            lowlink[x] = min(lowlink[x], lowlink[next]); //update low
        }
        else if(in_stack[next])
            lowlink[x] = min(lowlink[x], lowlink[next]); //update low
    }

    // out
    if(idx[x] == lowlink[x]) //head of scc
    {
        cc.clear();

        int y = S.top();
        S.pop(); in_stack[y] = 0;
        cc.push_back(y);

        while(y != x)
        {
            y = S.top();
            S.pop(); in_stack[y] = 0;
            cc.push_back(y);
        }

        ans.push_back(cc);
    }
}



int main()
{
    read();

    for(int i=1; i<=n; i++)
        if(idx[i] == -1)
            dfs(i);

    fout<<ans.size()<<'\n';
    for(auto &cc:ans)
    {
        for(auto &x:cc)
            fout<<x<<' ';
        fout<<'\n';
    }


    return 0;
}