#include<fstream>
#include<vector>
#include<list>

using namespace std;

int n,m;
struct node{
    int h, low;
    bool v, done;
};

vector<node> N;
vector<list<int> > G;

list<int> stack;
list<list<int> >result;


void visit(int x){
    N[x].v = true;
    N[x].h = stack.size();
    N[x].low = stack.size();
    stack.push_back(x);

    for(int y: G[x]){
        if(N[y].done) continue;

        if(!N[y].v)
            visit(y);
        N[x].low = min(N[x].low, N[y].low);
    }

    if(N[x].h == N[x].low){
        list<int> component;
        do{
            N[stack.back()].done=true;
            component.push_back(stack.back());
            stack.pop_back();
        }while(component.back() != x);

        result.push_back(move(component));
    }
}

void read(){
    int i=0, x, y;
    for(i=0; i<m; i++){
        scanf("%d %d",&x, &y);
        G[x].push_back(y);
    }
}

int main(){
    int i;
    freopen("ctc.in", "rt", stdin);
    freopen("ctc.out", "wt", stdout);
    
    scanf("%d %d",&n,&m);
    G.resize(n+1);
    N.resize(n+1);

    read();
    for(i=1; i<=n; i++){
        if(N[i].v == false)
            visit(i);
    }

    printf("%d\n", (int)result.size());
    while(result.size()){
        for(int x: result.front())
            printf("%d ", x);

        printf("\n");
        result.pop_front();
    }

    fclose(stdin);
    fclose(stdout);
    return 0;
}