#include <bits/stdc++.h>

using namespace std;

const int nmax = 1e5 + 10;

int n, m;
int used[nmax];
vector < int > g[nmax], gt[nmax];

int ans;
vector < int > all, curr;
vector < vector < int > > scc;

void input() {
    scanf("%d %d", &n, &m);
    for (int i = 1; i <= m; ++i) {
        int x, y; scanf("%d %d", &x, &y);

        g[x].push_back(y);
        gt[y].push_back(x);
    }
}

void dfs(int node) {
    used[node] = 1;
    for (auto &it: g[node]) {
        if (used[it]) continue;
        dfs(it);
    }

    all.push_back(node);
}

void dfst(int node) {
    used[node] = 1;
    for (auto &it: gt[node]) {
        if (used[it]) continue;
        dfst(it);
    }

    curr.push_back(node);
}

void compute_scc() {
    for (int i = 1; i <= n; ++i)
        if (!used[i]) dfs(i);
    reverse(all.begin(), all.end());

    memset(used, 0, sizeof(used));
    for (auto &node: all) {
        if (used[node]) continue;
        curr.clear(); dfst(node);
        ans++; scc.push_back(curr);
    }
}

void output() {
    printf("%d\n", ans);
    for (int i = 0; i < ans; ++i, printf("\n"))
        for (auto &it: scc[i]) printf("%d ", it);
}

int main() {
    freopen("ctc.in","r",stdin);
    freopen("ctc.out","w",stdout);

    input();
    compute_scc();
    output();

    return 0;
}