#include <fstream>
#include <algorithm>
#include <vector>
#include <stack>
using namespace std;
ifstream cin("ctc.in");
ofstream cout("ctc.out");
int n, m;
int use[100001];
vector<int> g[100001];
vector<int> gt[100001];
vector<int> s;
vector<vector<int>>ans;
vector<int> v;
void dfs1(int nod)
{
    use[nod] = 1;
   
    for(int i=0;i<g[nod].size();i++)
    {
        if(use[g[nod][i]]==0)
            dfs1(g[nod][i]);
    }
    s.push_back(nod);
}
void dfs2(int nod)
{
    use[nod] = -1;
    v.push_back(nod);
    for (int i = 0; i < gt[nod].size(); i++)
    {
        if (use[gt[nod][i]] == 1)
            dfs2(gt[nod][i]);
    }
}
int main()
{
    ios_base::sync_with_stdio(false);
    cin >> n >> m;
    for (int i = 1; i <= m; i++)
    {
        int x, y;
        cin >> x >> y;
        g[x].push_back(y);
        gt[y].push_back(x);
    }
    for (int i = 1; i <= n; i++)
    {
        if (use[i] == 0)
            dfs1(i);
    }
    for(int i=s.size()-1;i>=0;i--)
    {
        if (use[s[i]] == 1)
        {
            v.clear();
            dfs2(s[i]);
            ans.push_back(v);
        }
    }
    cout << ans.size() << "\n";
    for (auto i : ans)
    {
        for (auto j : i)
            cout << j << " ";
        cout << "\n";
    }
    return 0;
}