#include <bits/stdc++.h>

using namespace std;

const int kMaxN = 100005;

int n, m, nc;
int dfn[kMaxN], dfOrder;
bool onStack[kMaxN];
vector <int> graph[kMaxN];
vector <int> scc[kMaxN];
stack <int> sccStack;

int findScc(const int u) {
    dfOrder++;
    dfn[u] = dfOrder;
    int minPtr = dfOrder;
    sccStack.push(u);
    onStack[u] = true;
    for (const int v: graph[u]) {
        if (!dfn[v]) {
            minPtr = min(minPtr, findScc(v));
        }
        else if (onStack[v]) {
            minPtr = min(minPtr, dfn[v]);
        }
    }
    if (dfn[u] == minPtr) {
        int v;
        nc++;
        do {
            v = sccStack.top();
            sccStack.pop();
            onStack[v] = false;
            scc[nc].push_back(v);
        } while (v != u);
    }
    return minPtr;
}

int main() {
    freopen("ctc.in", "r", stdin);
    freopen("ctc.out", "w", stdout);
    
    scanf("%d %d", &n, &m);
    for (int i = 1; i <= m; i++) {
        int u, v;
        scanf("%d %d", &u, &v);
        graph[u].push_back(v);
    }
    
    for (int i = 1; i <= n; i++) {
        if (!dfn[i]) {
            findScc(i);
        }
    }
    
    printf("%d\n", nc);
    for (int i = 1; i <= nc; i++) {
        for (const int u: scc[i]) {
            printf("%d ", u);
        }
        printf("\n");
    }
    return 0;
}