#include <cstdio>
#include <algorithm>
#include <cstring>
#include <vector>
#define Nmax 100002
using namespace std;
int n, m, i, j, d[Nmax], c, scc[Nmax], nexti;
vector < int > V[Nmax], C[Nmax];
bool st[Nmax];

void read()
{
    int x, y;
    freopen("ctc.in", "r", stdin);
    freopen("ctc.out", "w", stdout);
    scanf("%d %d", &n, &m);
    for (i = 1; i <= m; ++ i)
    {
        scanf("%d %d", &x, &y);
        V[x].push_back(y);
    }
}
void dfs(int x)
{
    int i, l = V[x].size(), depth;
    d[x] = depth = ++ nexti;
    scc[++ scc[0]] = x;
    st[x] = 1;

    for (i = 0; i < l; ++ i)
        if (d[V[x][i]] == - 1)
        {
            dfs(V[x][i]);
            d[x] = min(d[x], d[V[x][i]]);
        }

        else
            if (st[V[x][i]])
               d[x] = min(d[x], d[V[x][i]]);

    if (d[x] == depth)
    {
        while (scc[0] > 0)
        {
            C[c].push_back(scc[scc[0]]);
            st[scc[scc[0]]] = 0;
            if (scc[scc[0]] == x)
            {
                -- scc[0];
                break;
            }
            -- scc[0];
        }
        ++ c;
    }
}
void solve()
{
    for (i = 0; i <= n; ++ i)
        d[i] = -1;
    for (i = 1; i <= n; ++ i)
        if (d[i] == -1)
            dfs(i);
}
void write()
{
    int l;
    printf("%d\n", c);
    for (i = 0; i < c; ++ i)
    {
        l = C[i].size();
        for (j = 0; j < l; ++ j)
            printf("%d ", C[i][j]);
        printf("\n");
    }
}
int main()
{
    read();
    solve();
    write();
    return 0;
}