#include<algorithm>
#include<bitset>
#include<cmath>
#include<cstdio>
#include<cstdlib>
#include<cstring>
#include<ctime>
#include<deque>
#include<fstream>
#include<iomanip>
#include<iostream>
#include<map>
#include<queue>
#include<set>
#include<stack>
#include<unordered_map>
#include<unordered_set>
#include<utility>
#include<vector>

using namespace std;

#define dbg(x) (cout<<#x<<" = "<<(x)<<'\n')
#ifdef HOME
const string inputFile = "input.txt";
const string outputFile = "output.txt";
#else
const string problemName = "ctc";
const string inputFile = problemName + ".in";
const string outputFile = problemName + ".out";
#endif // HOME

typedef long long int lld;
typedef pair<int, int> PII;
typedef pair<int, lld> PIL;
typedef pair<lld, int> PLI;
typedef pair<lld, lld> PLL;

const int INF = (1LL << 30) - 1;
const lld LINF = (1LL << 62) - 1;
const int dx[] = {1, 0, -1, 0, 1, -1, 1, -1};
const int dy[] = {0, 1, 0, -1, 1, -1, -1, 1};
const int MOD = (int)(1e9) + 7;

const int NMAX = 100000 + 5;
const int MMAX = 100000 + 5;
const int KMAX = 100000 + 5;
const int PMAX = 100000 + 5;
const int LMAX = 100000 + 5;
const int VMAX = 100000 + 5;

int N, M, nrCTC;
vector<int> V[NMAX];
vector<int> Vt[NMAX];
vector<int> CTC[NMAX];
int ST[NMAX], top;
bitset<NMAX> viz;

void dfs_1(int x) {
    viz[x] = 1;
    for(auto y : V[x])
        if(!viz[y])
            dfs_1(y);
    ST[++top] = x;
}

void dfs_2(int x) {
    viz[x] = 0;
    CTC[nrCTC].push_back(x);
    for(auto y : Vt[x])
        if(viz[y])
            dfs_2(y);
}

int main() {
    int i, x, y;

#ifndef ONLINE_JUDGE
    freopen(inputFile.c_str(), "r", stdin);
    freopen(outputFile.c_str(), "w", stdout);
#endif

    scanf("%d%d", &N, &M);

    while(M--) {
        scanf("%d%d", &x, &y);
        V[x].push_back(y);
        Vt[y].push_back(x);
    }

    for(i = 1; i <= N; i++)
        if(!viz[i])
            dfs_1(i);

    for(i = N; i >= 1; i--)
        if(viz[ST[i]]) {
            nrCTC++;
            dfs_2(ST[i]);
        }

    printf("%d\n", nrCTC);

    for(i = 1; i <= nrCTC; i++) {
        for(auto x : CTC[i])
            printf("%d ", x);
        printf("\n");
    }

    return 0;
}