#include <bits/stdc++.h>

using namespace std;

const int nmax = 1e5 + 10;

int n, m, ans;
bool used[nmax];
vector < int > g[nmax], gt[nmax], st, v[nmax];

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);
    }

    st.push_back(node);
}

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

    v[ans].push_back(node);
}

void get_scc() {
    for (int i = 1; i <= n; ++i)
        if(!used[i]) dfs(i);

    memset(used, 0, sizeof(used));
    for (auto it = st.rbegin(); it != st.rend(); ++it) {
        if (used[*it]) continue;
        ans++; dfsT(*it);
    }
}

void output() {
    printf("%d\n", ans);
    for (int idx = 1; idx <= ans; ++idx, printf("\n"))
        for (auto &it: v[idx])
            printf("%d ", it);
}

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

    input();
    get_scc();
    output();

    return 0;
}