#include <cstdio>
#include <vector>

using namespace std;

const int NMAX = 100000;

vector <int> v[NMAX+5];
int idx[NMAX+5], low[NMAX+5];
bool instack[NMAX+5];

int Stack[NMAX+5], Size;

int index = 1;

int comp;
vector <int> ans[NMAX+5];

void tarjan(int nod)
{
    idx[nod] = index++;
    low[nod] = idx[nod];
    Stack[Size++] = nod;
    instack[nod] = true;
    for(int i=0; i<v[nod].size(); i++)
        if(idx[v[nod][i]] == 0)
        {
            tarjan(v[nod][i]);
            low[nod] = min(low[nod], low[v[nod][i]]);
        }
        else if(instack[v[nod][i]])
        {
            low[nod] = min(low[nod], idx[v[nod][i]]);
        }
    if(idx[nod] == low[nod])
    {
        do
        {
            Size--;
            instack[Stack[Size]] = false;
            ans[comp].push_back(Stack[Size]);
        }
        while(Size>=0 && Stack[Size] != nod);
        comp++;
    }
}

int main()
{
    freopen("ctc.in", "r", stdin);
    freopen("ctc.out", "w", stdout);
    int n, m;
    scanf("%d%d", &n, &m);
    for(int i=0; i<m; i++)
    {
        int x, y;
        scanf("%d%d", &x, &y);
        v[x].push_back(y);
    }
    for(int i=1; i<=n; i++)
        if(idx[i] == 0)
            tarjan(i);
    printf("%d\n", comp);
    for(int i=0; i<comp; i++)
    {
        for(auto x : ans[i])
            printf("%d ", x);
        printf("\n");
    }
    return 0;
}