#include <bits/stdc++.h>
#define NMAX 100009
using namespace std;
ifstream fin("ctc.in");
ofstream fout("ctc.out");
vector <int>g[NMAX];
vector <int>gt[NMAX];
vector <int>sol[NMAX];
int  uz[NMAX], lowlink[NMAX], cnt, cnt1;
int i,lg,nr,n,j,m;
int s[NMAX];
void citire();
void dfs(int k);
void reset();
int main()
{citire();
    for(i=1; i<=n; i++)
        if(!uz[i]) dfs(i);
    fout<<nr<<'\n';
    for(i=1; i<=nr; i++)
    { for(j=0; j<sol[i].size(); j++)
            fout<<sol[i][j]<<" ";
        fout<<'\n';
    } return 0;
}
void citire()
{
    int i,j,x,y;
    fin>>n>>m;
    for(i=1; i<=m; i++)
    { fin>>x>>y;
        g[x].push_back(y); gt[y].push_back(x);
    }
}
void dfs(int k)
{  int i;
    uz[k]= ++cnt;
    lowlink[k] = cnt;
    s[++lg]=k;
    for(i=0; i<g[k].size(); i++)
    {if(!uz[g[k][i]])
            dfs(g[k][i]);
        if(uz[g[k][i]] > 0)
            lowlink[k] = min(lowlink[k],lowlink[g[k][i]]);
    }
    if(uz[k] == lowlink[k])
    {nr++;
        do{
        sol[nr].push_back(s[lg]); uz[s[lg]]=-1;
        }
        while(s[lg--]!=k);
    }
}
void reset()
{int i;
    for(i=0; i<NMAX; i++) uz[i]=0;
}