#include <bits/stdc++.h>

using namespace std;

const int maxn = 1e5 + 5;

int N, M;
vector <int> v[maxn], inv[maxn];
int top[maxn];
bool viz[maxn];
vector <int> ctc[maxn];

void topo(int nod)  {
    if(viz[nod])
        return;
    viz[nod] = 1;
    for(auto x : v[nod])
        topo(x);
    top[++top[0]] = nod;
}

void dfs(int nod)  {
    if(!viz[nod])
        return;
    viz[nod] = 0;
    for(auto x : inv[nod])
        dfs(x);
    ctc[ctc[0]].push_back(nod);
}

int main()  {
    freopen("ctc.in", "r", stdin);
    freopen("ctc.out", "w", stdout);
    cin >> N >> M;
    for(int i = 1;i <= M;i++)  {
        int x, y;
        cin >> x >> y;
        v[x].push_back(y);
        inv[y].push_back(x);
    }
    topo(1);
    ctc[0] = 1;
    for(int i = top[0];i >= 1;i--)  {
        if(viz[top[i]] == 1)  {
            dfs(top[i]);
            ctc[0]++;
        }
    }
    ctc[0]--;
    cout << ctc[0] << "\n";
    for(int i = 1;i <= ctc.size();i++)  {
        for(auto x : ctc[i])
            cout << x << " ";
        cout << "\n";
    }
    return 0;
}