Description：

Solution：

Code：

#include<algorithm>

#include<iostream>

#include<cstdlib>

#include<cstdio>

#include<cmath>

#include<queue>

#include<cstring>

using namespace std;

int n,m;

#define MAXN 110

#define MAXM 1010

int a[MAXM],b[MAXM];

int s,t;

#define INF 100000000000 

struct edge

{

	int to,nxt;

	long double f;

}e[MAXM * 2 + MAXN * 2 + MAXM * 2 * 2];

int edgenum = 0;

int lin[MAXN + MAXM];

void add(int a,int b,long double k)

{

	e[edgenum].to = b;e[edgenum].f = k;e[edgenum].nxt = lin[a];lin[a] = edgenum;++edgenum;

	e[edgenum].to = a;e[edgenum].f = 0;e[edgenum].nxt = lin[b];lin[b] = edgenum;++edgenum;

	return;

}

int ch[MAXN + MAXM];

#define eps 1e-18 

bool BFS()

{

	queue<int> q;q.push(s);

	memset(ch,-1,sizeof(ch));ch[s] = 0;

	while(!q.empty())

	{

		int k = q.front();q.pop();

		for(int i = lin[k];i != -1;i = e[i].nxt)

		{

			if(ch[e[i].to] == -1 && e[i].f >= eps)

			{

				ch[e[i].to] = ch[k] + 1;

				q.push(e[i].to);

			}

		}

	}

	return (ch[t] != -1);

}

long double flow(int k,long double f)

{

	if(k == t)return f;

	long double r = 0;

	for(int i = lin[k];i != -1 && f > r;i = e[i].nxt)

	{

		if(ch[e[i].to] == ch[k] + 1 && e[i].f >= eps)

		{

			long double l = flow(e[i].to,min(f - r,e[i].f));

			e[i].f -= l;r += l;e[i ^ 1].f += l;

		}

	}

	if(r <= eps)ch[k] = -1;

	return r;

}

long double dinic()

{

	long double ans = 0,r;

	while(BFS())while((r = flow(s,1000000000000)) > eps)ans += r;

	return ans;

}

bool check(long double x)

{

	memset(lin,-1,sizeof(lin));

	edgenum = 0;

	s = n + m + 1,t = s + 1;

	for(int i = 1;i <= m;++i)add(s,i + n,1);

	for(int i = 1;i <= n;++i)add(i,t,x);

	for(int i = 1;i <= m;++i)

	{

		add(i + n,a[i],INF);

		add(i + n,b[i],INF);

	}

	long double res = m - dinic();

	if(res >= eps)return true;

	else return false;

}

vector<int> v;

int main()

{

	scanf("%d%d",&n,&m);

	for(int i = 1;i <= m;++i)scanf("%d%d",&a[i],&b[i]);

	long double l = 0,r = 1000000000000,mid;

	long double ans = 0; 

	while(r - l >= 1e-5)

	{

		mid = (l + r) / 2;

		if(check(mid))

		{

			ans = mid;

			l = mid;

		}

		else r = mid;

	}

	check(ans);

	for(int i = lin[t];i != -1;i = e[i].nxt)

	{

		if(e[i ^ 1].f <= eps)v.push_back(e[i].to);

	}

	sort(v.begin(),v.end());

	cout << v.size() << endl;

	for(vector<int>::iterator i = v.begin();i != v.end();++i)

	{

		printf("%d\n",*i);

	}

	return 0;

}