#include<algorithm>

#include<iostream>

#include<cstdlib>

#include<cstdio>

#include<cmath>

#include<queue>

#include<cstring>

using namespace std;

int n,m;

#define MAXN 1010

#define MAXM 3010

struct edge

{

	int to,nxt,l,r;

}e[MAXM << 1];

int edgenum = 0;

int lin[MAXN] = {0};

void add(int a,int b,int l,int r)

{

	++edgenum;e[edgenum].to = b;e[edgenum].l = l;e[edgenum].r = r;e[edgenum].nxt = lin[a];lin[a] = edgenum;

	++edgenum;e[edgenum].to = a;e[edgenum].l = l;e[edgenum].r = r;e[edgenum].nxt = lin[b];lin[b] = edgenum;

	return;

}

int d[MAXN];

bool v[MAXN];

int s[MAXM],tot = 0;

int main()

{

	freopen("travel.in","r",stdin);

	freopen("travel.out","w",stdout);

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

	int a,b,l,r;

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

	{

		scanf("%d%d%d%d",&a,&b,&l,&r);

		add(a,b,l,r);

		s[++tot] = l;

	}

	sort(s + 1,s + 1 + tot);

	int ans = 0;

	int left;

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

	{

		memset(d,0,sizeof(d));

		memset(v,false,sizeof(v));

		d[1] = 0x3f3f3f3f;

		queue<int> q;

		q.push(1);

		while(!q.empty())

		{

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

			v[k] = false;

			for(int i = lin[k];i != 0;i = e[i].nxt)

			{

				if(e[i].l <= s[t] && d[e[i].to] < min(d[k],e[i].r))

				{

					d[e[i].to] = min(d[k],e[i].r);

					if(!v[e[i].to])

					{

						v[e[i].to] = true;

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

					}

				}

			}

		}

		if(d[n] - s[t] + 1 > ans)

		{

			ans = d[n] - s[t] + 1;

			left = s[t];

		}

	}

	cout << ans << endl;

	for(int i = left;i <= left + ans - 1;++i)printf("%d ",i);puts("");

	fclose(stdin);

	fclose(stdout);

	return 0;

}