#include<cstdio>
#include<vector>
using namespace std;

 int n,m;
vector <int> vec[10001];
vector <int> q;
vector <int> sol[10001];

int viz[10001];
int tata[10001];
int nivel[10001];
int nrcomp;

void read()
{
	int i,j,x,y;
	scanf("%d %d",&n,&m);
	for (i=1;i<=n;++i)
	{	scanf("%d %d",&x,&y);
	  vec[x].push_back(y);
	  vec[y].push_back(x);
	}
}



void dfs (int nod,int niv,int tata)
{
	q.push_back(nod);
	viz[nod]=niv;

	for (int i=0;i<vec[nod].size();++i)
    {
        int x=vec[nod][i];
	 if (viz[x]==0)
        {
            q.push_back(nod);
			int k=nod;
			tata[x]=k;
            dfs(x,niv,nod);

            if (viz[nod]>viz[x])
               viz[nod]=viz[x];
	    } 
		else
			if (tata[x]!=nod)
			{ viz[nod]=viz[x];
                if (viz[x]<=niv)
		{
                    int m=q.size();
			m--;
                    int j;
                    nrcomp++;

                    while (nod!=q[m])
					{
					printf("%d",q[m]);
			      q.pop_back();
					}
			
           }
        }
}

}


void write()
{
	int i,j;
printf("%d",nrcomp);
        for ( i=1;i<=nrcomp;i++)
	{
            for (j=0;j<sol[i].size();++j)
                printf("%d",sol[i][j]);
	            
}
         
}


int main()
{
	int i;
	freopen("biconexe.in","r",stdin);
	freopen("biconexe.out","w",stdout);
	read();
	for (i=1;i<=n;++i) if (!nivel[i]) dfs(i,1,0);
		
write();
}