#include <iostream>
#include <cstring>
#include <vector>
#include <cstdio>
#define N 100005

using namespace std;

int n, m, viz1[N], viz2[N], nr;
vector <int> graf1[N], graf2[N], a;

void citire()
{
    scanf("%d %d\n", &n, &m);
    for(int i=1;i<=m;i++)
    {
        int x, y;
        scanf("%d %d\n", &x, &y);
        graf1[x].push_back(y);
        graf2[y].push_back(x);
    }
}

void dfs(int x)
{
    viz1[x]=1;
    for(int i=0;i<graf1[x].size();i++)
    {
        int nod=graf1[x][i];
        if(!viz1[nod])
            dfs(nod);
        a.push_back(nod);
    }
}

void dfs_inv(int x)
{
    viz2[x]=nr;
    for(int i=0;i<graf2[x].size();i++)
    {
        int nod=graf2[x][i];
        if(!viz2[nod])
            dfs_inv(nod);
    }
}

void afisare()
{
    for(int i=1;i<=nr;i++)
        for(int j=1;j<=n;j++)
            if(viz2[j]==i)
                printf("%d ", j);
}

int main()
{
    freopen("ctc.in", "r", stdin);
//    freopen("ctc.out", "w", stdout);

    citire();
    for(int i=1;i<=n;i++)
        if(!viz1[i])
            dfs(i);
    for(int i=0;i<a.size();i++)
        if(!viz2[a.back()])
        {
            nr++;
            dfs_inv(a.back());
            a.pop_back();
        }
    printf("%d\n", nr);
    afisare();
    return 0;
}