#include <stdio.h>
#include <vector>
#define max 100010
using namespace std;
vector<int> g[max],comp[max];
int n,m,stack[max],top,stack2[max],I[max],top2,c,i,j;
void dfs(int v)//gabow
{
    stack[++top]=v; I[v]=top; stack2[++top2]=I[v];
    for(int i=0; i<g[v].size(); i++)
     if(I[g[v][i]]==0) dfs(g[v][i]);
     else while(I[g[v][i]]<stack2[top2]) top2--;
    if(I[v]==stack2[top2])
    {
        top2--;
        c++;
        while(I[v]<=top) { I[stack[top]]=c; comp[c-n].push_back(stack[top--]); }
    }
}
int main()
{
    freopen("ctc.in","r",stdin);
    freopen("ctc.out","w",stdout);
    scanf("%d%d",&n,&m);
    for(; m>0; m--)
    {
        scanf("%d%d",&i,&j);
        g[i].push_back(j);
    }
    c=n;
    for(i=1; i<=n; i++)
     if(!I[i]) dfs(i);
    printf("%d\n",c-n);
    for(i=1; i<=c-n; i++)
    {
        for(j=0; j<comp[i].size(); j++)
         printf("%d ",comp[i][j]);
        printf("\n");
    }
    return 0;
}