#include <bits/stdc++.h>

template <class T>
inline void read(T &res)
{
	char ch; bool flag = false; res = 0;
	while (ch = getchar(), !isdigit(ch) && ch != '-');
	ch == '-' ? flag = true : res = ch ^ 48;
	while (ch = getchar(), isdigit(ch))
		res = res * 10 + ch - 48; 
}

template <class T>
inline void put(T x)
{
	if (x > 9) put(x / 10);
	putchar(x % 10 + 48); 
}
 
const int N = 1e6 + 5;
const int N2 = 2e6 + 5;
int cur[N], adj[N], dis[N], nxt[N2], to[N2], cst[N2], from[N2];
int n, q, T = 1, cm; bool vis[N], istree[N2];

template <class T>
inline T Abs(T x) {return x < 0 ? -x : x;}

inline void linkArc(int x, int y, int z)
{
	nxt[++T] = adj[x]; adj[x] = T; from[T] = x; to[T] = y; cst[T] = z;
	nxt[++T] = adj[y]; adj[y] = T; from[T] = y; to[T] = x; cst[T] = -z;
}

inline void dfs(int x)
{
	vis[x] = true;
	int y;
	for (int e = adj[x]; e; e = nxt[e])
		if (!vis[y = to[e]])
		{
			istree[e] = istree[e ^ 1] = true;
			dis[y] = dis[x] + cst[e];
			dfs(y);
		}
}

int main()
{
	read(n); read(q);
	for (int i = 1, x, y; i <= q; ++i)
	{
		read(x); read(y);
		linkArc(x, y, 1);
	}
	for (int i = 1; i <= n; ++i)
		if (!vis[i])
		{
			dis[i] = 0;
			dfs(i);	
		}
	int m =  0;
	for (int e = 2; e <= T; ++e)
		if (!istree[e])
			m = std::__gcd(m, Abs(dis[from[e]] + cst[e] - dis[to[e]]));
	if (m == 0)
	{
		put(n), putchar('\n');
		for (int i = 1; i <= n; ++i)
			put(i), putchar(' ');
	}
	else 
	{
		for (int i = 1; i <= n && i <= m; ++i)
			if (m % i == 0)
				cur[++cm] = i;	
		put(cm), putchar('\n');
		for (int i = 1; i <= cm; ++i)
			put(cur[i]), putchar(' ');
	}
}