#include <bits/stdc++.h>

using namespace std;
ifstream in("ctc.in");
ofstream out("ctc.out");
int n, m;
vector<int> adj[100005];
int found[100005], low[100005];
int x, y;
vector<int> comp[100005];
int t;
int st[100005], top;
int nrc;
bool inst[100005];

void dfs(int nod) {
    //cout << nod << '\n';
    found[nod] = t;
    low[nod] = t;
    t++;
    st[++top] = nod;
    inst[nod] = 1;

    for (auto it : adj[nod]) {
        if (found[it] == 0) {
            dfs(it);
            low[nod] = min(low[nod], low[it]);
        } else {
            if (inst[it]) {
                low[nod] = min(low[nod], found[it]);
            }
        }
    }

    if (low[nod] == found[nod]) {
        nrc++;
        do {
            comp[nrc].push_back(st[top]);
            top--;
        } while (st[top] != nod);
        comp[nrc].push_back(st[top]);
        top--;
    }
}

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

    for (int i = 1; i <= n; i++) {
        if (found[i] == 0) {
            t = 1;
            top = 0;
            dfs(i);
        }
    }

    out << nrc << '\n';
    for (int i = 1; i <= nrc; i++) {
        for (auto it : comp[i])
            out << it << " ";
        out << '\n';
    }
    return 0;
}