#include<bits/stdc++.h>
#pragma GCC optimize("Ofast,unroll-loops,inline")
#pragma GCC target("avx2,bmi,bmi2,lzcnt,popcnt")
#define fast ios_base::sync_with_stdio(0);cin.tie(0);cout.tie(0);
#define setinf(x) memset(x,0x3f3f3f3f,sizeof(x));
#define set0(x) memset(x,0,sizeof(x));
#define all(x) x.begin(),x.end()
#define pii pair<int,int>
#define INF 0x3f3f3f3f
#define vi vector<int>
#define ll long long
#define vll vector<ll>
#define pb push_back
#define fi first
#define se second
#define DD 100001
#define nl '\n'
using namespace std;
const string file="ctc";
ifstream f(file+".in");
ofstream g(file+".out");
//#define f cin
//#define g cout
int n,m,comp,t;
vi v[DD],r[DD];
int low[DD],id[DD],on[DD];
stack<int>s;
void dfs(int x) {
    id[x]=low[x]=t++;
    on[x]=1;
    s.push(x);
    for (auto e:v[x]) {
        if (!id[e]) dfs(e);
        if (on[e]) low[x]=min(low[x],low[e]);
    }
    if (id[x]==low[x]) {
        int top;
        ++comp;
        do {
            top=s.top();
            s.pop();
            r[comp].pb(top);
            on[top]=0;
            low[top]=id[x];
        }while (top!=x);
    }
}
int main(){
    f>>n>>m;
    for (int i=1; i<=m; ++i) {
        int x,y;
        f>>x>>y;
        v[x].pb(y);
    }
    for (int i=1; i<=n; ++i) {
        if (!id[i]) dfs(i);
    }
    g<<comp<<nl;
    for (int i=1; i<=comp; ++i,g<<nl) {
        for (auto e:r[i]) g<<e<<' ';
    }
    system("pause");
    return 0;
}