#include <fstream>
#include <vector>
#include <stack>
using namespace std;

class InputReader
{
    public:
        InputReader() {}
        InputReader(const char* file_name)
        {
            input_file = fopen(file_name,"r");
            cursor = 0;
            fread(buff,SIZE,1,input_file);
        }

        inline InputReader &operator >>(int& n)
        {
            n = 0;
            while (buff[cursor] < '0' || buff[cursor] > '9')
                advance();
            while (buff[cursor] >= '0' && buff[cursor] <= '9') {
                n = n * 10 + buff[cursor] - '0';
                advance();
            }
            return *this;
        }

    private:
        static const int SIZE = 1<<17;
        int cursor;
        FILE *input_file;
        char buff[SIZE];

        inline void advance() {
            cursor++;
            if (cursor == SIZE) {
                cursor = 0;
                fread(buff,SIZE,1,input_file);
            }
        }
};

int n,m;
vector<int> G[100001];
vector< vector<int> > Comp;
stack<int> ST;
bool seen[100001];
int Idx = 0,lowlink[100001],idx[100001];

int dfs(int node)
{
    seen[node] = 1;
    idx[node] = ++Idx;
    lowlink[node] = Idx;
    ST.push(node);

    for (int i = 0; i < G[node].size(); i++)
    {
        if (seen[G[node][i]])
        {
            lowlink[node] = min(lowlink[node],idx[G[node][i]]);
        }
        else
        {
            dfs(G[node][i]);
            lowlink[node] = min(lowlink[node],lowlink[G[node][i]]);
        }
    }

    if (idx[node] == lowlink[node])
    {
        Comp.push_back(vector<int>());
        while (ST.top() != node) {
            Comp.back().push_back(ST.top());
            ST.pop();
        }
        ST.pop();
        Comp.back().push_back(node);
    }
}

void Tarjan()
{
    for (int i = 1; i <= n; i++)
        if (!seen[i])
            dfs(i);
}

int main()
{
    InputReader fin = InputReader("ctc.in");
    ofstream fout("ctc.out");

    int x,y;
    fin >> n >> m;
    for (int i = 1; i <= m; i++)
    {
        fin >> x >> y;
        G[x].push_back(y);
    }

    Tarjan();

    fout << Comp.size() << "\n";
    for (int i = 0; i < Comp.size(); i++) {
        for (int j = 0; j < Comp[i].size(); j++)
            fout << Comp[i][j] << " ";
        fout << "\n";
    }
}