#include <fstream>
#include <stack>
#include <vector>
#define NMAX 100001
using namespace std;
ifstream cin("ctc.in");
ofstream cout("ctc.out");
vector<int> g[NMAX];
vector<int> af[NMAX];
vector<int> ig[NMAX];
char viz[NMAX];
stack<int> st;
int n,m,x,y,cnt;
void DFS1(int x)
{
    viz[x]=1;
    for(size_t i=0; i<g[x].size(); ++i)
        if(viz[g[x][i]]==0) DFS1(g[x][i]);
    st.push(x);
}
void DFS2(int x)
{
    af[cnt].push_back(x);
    viz[x]=0;
    for(size_t i=0; i<ig[x].size(); ++i)
        if(viz[ig[x][i]]==1) DFS2(ig[x][i]);
}
void solve()
{
    cin>>n>>m;
    for(int i=1; i<=m; ++i)
    {
        cin>>x>>y;
        g[x].push_back(y);
        ig[y].push_back(x);
    }
    for(int i=1; i<=n; ++i)
        if(viz[i]==0) DFS1(i);
    while(!st.empty())
    {
        x=st.top();
        st.pop();
        if(viz[x]==1)
        {
            cnt++;
            DFS2(x);
        }
    }
    cout<<cnt<<"\n";
    for(int j=1; j<=cnt; ++j)
    {
        for(size_t i=0; i<af[j].size(); ++i)
            cout<<af[j][i]<<" ";
        cout<<"\n";
    }
}
int main()
{
    solve();
    return 0;
}