#include<cstdio>
#include<vector>
#include<stack>

using namespace std;

const int nmax=1e5+5;

vector<int> g[nmax],gt[nmax],temp;
vector< vector<int> > sol;
bool viz[nmax],viz2[nmax];
stack<int>st;

inline void dfs(int node)
{
    viz[node]=1;
    int i,cnode;
    for(i=0;i<g[node].size();++i)
    {
        cnode=g[node][i];
        if(!viz[cnode])
            dfs(cnode);
    }
    st.push(node);
}

inline void dfs2(int node)
{
    viz2[node]=1;
    int i,cnode;
    for(i=0;i<gt[node].size();++i)
    {
        cnode=gt[node][i];
        if(!viz2[cnode])
            dfs2(cnode);
    }
    temp.push_back(node);
}

int main()
{
    freopen("ctc.in","r",stdin);
    freopen("ctc.out","w",stdout);
    int m,n,i,j;
    scanf("%d%d",&n,&m);
    int x,y;
    for(i=1;i<=m;++i)
    {
        scanf("%d%d",&x,&y);
        g[x].push_back(y);
        gt[y].push_back(x);
    }
    for(i=1;i<=n;++i)
        if(!viz[i])
            dfs(i);
    int node,cnt=0;
    while(!st.empty())
    {
        node=st.top();
        st.pop();
        if(!viz2[node])
        {
            temp.clear();
            dfs2(node);
            cnt++;
            sol.push_back(temp);
        }
    }
    printf("%d\n",cnt);
    for(i=0;i<cnt;++i)
    {
        for(j=0;j<sol[i].size();++j)
            printf("%d ",sol[i][j]);
        printf("\n");
    }
}