#include <bits/stdc++.h>


using namespace std;

class InParser
{
private:
    FILE *fin;
    char *buff;
    int sp;

    char read_ch()
    {
        ++sp;
        if(sp==4096)
        {
            sp=0;
            fread(buff,1,4096,fin);
        }
        return buff[sp];
    }

public:
    InParser(const char* nume)
    {
        fin=fopen(nume,"r");
        buff=new char[4096]();
        sp=4095;
    }

    InParser& operator >> (int &n)
    {
        char c;
        while(!isdigit(c=read_ch())&&c!='-');
        int sgn=1;
        if (c=='-')
        {
            n=0;
            sgn=-1;
        }
        else
        {
            n=c-'0';
        }
        while(isdigit(c=read_ch()))
        {
            n=10*n+c-'0';
        }
        n*=sgn;
        return *this;
    }

    InParser& operator >> (long long &n)
    {
        char c;
        n=0;
        while(!isdigit(c=read_ch())&&c!='-');
        long long sgn=1;
        if(c=='-')
        {
            n=0;
            sgn=-1;
        }
        else
        {
            n=c-'0';
        }
        while(isdigit(c=read_ch()))
        {
            n=10*n+c-'0';
        }
        n*=sgn;
        return *this;
    }
};

class OutParser
{
private:
    FILE *fout;
    char *buff;
    int sp;

    void write_ch(char ch)
    {
        if(sp==50000)
        {
            fwrite(buff,1,50000,fout);
            sp=0;
            buff[sp++]=ch;
        }
        else
        {
            buff[sp++]=ch;
        }
    }

public:
    OutParser(const char* name)
    {
        fout=fopen(name,"w");
        buff=new char[50000]();
        sp=0;
    }
    ~OutParser()
    {
        fwrite(buff,1,sp,fout);
        fclose(fout);
    }

    OutParser& operator <<(int vu32)
    {
        if(vu32<=9)
        {
            write_ch(vu32+'0');
        }
        else
        {
            (*this) <<(vu32/10);
            write_ch(vu32%10+'0');
        }
        return *this;
    }

    OutParser& operator <<(long long vu64)
    {
        if(vu64<=9)
        {
            write_ch(vu64+'0');
        }
        else
        {
            (*this) <<(vu64/10);
            write_ch(vu64%10+'0');
        }
        return *this;
    }

    OutParser& operator <<(char ch)
    {
        write_ch(ch);
        return *this;
    }
    OutParser& operator <<(const char *ch)
    {
        while(*ch)
        {
            write_ch(*ch);
            ++ch;
        }
        return *this;
    }
};
InParser f ("ctc.in");
OutParser g ("ctc.out");

int n, m, x, y, viz[100005], nr;
vector < int > G[100005], GT[100005], CTC[100005];
stack < int > S;

void read () {
    f >> n >> m;
    while (m --) {
        f >> x >> y;
        G[x].push_back (y);
        GT[y].push_back (x);
    }
}

void DFSP (int k) {
    viz[k] = 1;
    for (unsigned int i = 0; i < G[k].size(); ++i) {
        int vecin = G[k][i];
        if (!viz[vecin]) DFSP (vecin);
    }
    S.push (k);
}

void DFSM (int k) {
    viz[k] = 2;
    CTC[nr].push_back (k);
    for (unsigned int i = 0; i < GT[k].size(); ++i) {
        int vecin = GT[k][i];
        if (viz[vecin] == 1) DFSM (vecin);
    }
}

void solve () {
    for (int i = 1; i <= n; ++i) if (!viz[i]) DFSP (i);
    while (!S.empty()) {
        int nod = S.top();
        S.pop();
        if (viz[nod] == 1) {
            nr ++;
            DFSM (nod);
        }
    }
}

void print () {
    g << nr << '\n';
    for (int i = 1; i <= nr; ++i, g << '\n')
    for (unsigned int j = 0; j < CTC[i].size(); ++j)
    g << CTC[i][j] << " ";
}

int main()
{
    read();
    solve();
    print();
    return 0;
}