#include <stdio.h>
#include <stdlib.h>
#include <ctype.h>
#include <algorithm>
#include <vector>

using namespace std;

FILE *fin = fopen("ctc.in", "r");
FILE *fout = fopen("ctc.out", "w");

#define BUF 1 << 17
char buf[BUF];
int pos = BUF;

inline char next()  {
    if(pos == BUF)
        fread(buf, 1, BUF, fin), pos = 0;
    return buf[pos++];
}

inline int read()  {
    int x = 0;
    char ch = next();
    while(!isdigit(ch))
        ch = next();
    while(isdigit(ch))
        x = x * 10 + ch - '0', ch = next();
    return x;
}

#define MAX_N 100000
#define MAX_M 200000

int n, m;
vector <int> v[MAX_N + 1];
vector <int> sol[MAX_N + 1];
vector <int> stk;

int idx[MAX_N + 1];
int freeidx = 0;
bool ostk[MAX_N + 1];
int numCTC = 0;

int tarjan(int nod)  {
    int minPtr = idx[nod] = ++freeidx;
    stk.push_back(nod);
    ostk[nod] = 1;
    for(auto &son : v[nod])
        if(!idx[son])
            minPtr = min(minPtr, tarjan(son));
        else if(ostk[son])
            minPtr = min(minPtr, idx[son]);
    if(idx[nod] == minPtr)  {
        int aux;
        do  {
            aux = stk[stk.size() - 1];
            ostk[aux] = 0;
            stk.pop_back();
            sol[numCTC].push_back(aux);
        }  while(aux != nod);
        numCTC++;
    }
    return minPtr;
}

int main()  {
    int i, x, y;
    n = read(), m = read();
    for(i = 1;i <= m;i++)  {
        x = read(), y = read();
        v[x].push_back(y);
    }
    for(i = 1;i <= n;i++)
        if(!idx[i])
            tarjan(i);
    fprintf(fout, "%d\n", numCTC);
    for(i = 0;i < numCTC;i++)  {
        for(auto &nod: sol[i])
            fprintf(fout, "%d ", nod);
        fputc('\n', fout);
    }
    fclose(fin);
    fclose(fout);
    return 0;
}