#include <bits/stdc++.h>

using namespace std;

int n, m, x, y;
int  v[100005];
int  ll[100005];
bool ins[100005];
vector<vector<int>> T;

struct node{
    node *next;
    int inf;
};
node *L[100005];

void add(node *&start, int inf) {
    node *one = new node;
    one->inf = inf;
    one->next = start;
    start = one;
}

stack<int> s;
int nr;

void dfs(int in) {
    nr ++;
    v[in] = nr;
    ll[in] = nr;
    s.push(in);
    ins[in] = true;

    for(node *p = L[in]; p; p = p->next) {
        if(!v[p->inf]) {
            dfs(p->inf);
            ll[in] = min(ll[in], ll[p->inf]);
        }
        else if(ins[p->inf]) {
            ll[in] = min(ll[in], ll[p->inf]);
        }
    }
    if(v[in] == ll[in]) {
        vector<int> ans;
        ans.clear();
        int i;
        do {
            i = s.top();
            s.pop();
            ans.push_back(i);
            ins[i] = false;
        }
        while(i != in);
        T.push_back(ans);
    }
}

int main()
{
    FILE *f = fopen("ctc.in", "r");
    FILE *g = fopen("ctc.out", "w");
    fscanf(f, "%d %d", &n, &m);
    for(int i = 1; i <= m; i ++) {
        fscanf(f, "%d %d", &x, &y);
        add(L[x], y);
    }

    for(int i = 1; i <= n; i ++) {
        if(!v[i]) {
            dfs(i);
        }
    }
    fprintf(g, "%d\n", T.size());
    for(int j = 0; j < T.size(); j ++) {
        for(int i = 0; i < T[j].size(); i ++)
            fprintf(g, "%d ", T[j][i]);
        fprintf(g, "\n");
    }
    return 0;
}