#include<iostream>
#include<cstring>
using namespace std;

const long maxn = 20000 + 100;
const long maxm = 500000 + 100;
int g[maxn][maxn];
int n, m, count, z, ans;
int u[maxm], v[maxm], a[maxn];

void fun()
{
	memset(a, 0, sizeof(a));
	for (int i =1; i <= n; i++)
	{
		count = 0;
		for (int j = 1; j <= n; j++)
		{
			if (g[i][j] == 1)
				count++;
		}
		if (count >= 3)
			a[i] = 1;
	}
}

int main()
{
	freopen("asm_game.in","r",stdin);
	freopen("asm_game.out","w",stdout);
	memset(g, 0, sizeof(g));
	cin >> n >> m;
	int cnt = n;
	for (int i = 1; i <= m; i++)
	{
		cin >> u[i] >> v[i];
		g[u[i]][v[i]] = 1;
		g[v[i]][u[i]] = 1;
	}
	fun();
	for (int i = 1; i <= n; i++)
	{
		z = 0;
		if (a[i] == 1)
			z++;
		else
		{
			for (int j = 1; j <= n; j++)
			{
				g[i][j] = 0;
				g[j][i] = 0;
			}
			cnt--;
		}
		if (z != cnt || cnt != 0)
			fun();
		else
			break;
	}
	if (cnt == 0)
		ans = 0;
	else
		for (int i = n; i >= 1; i--)
		{
			if (a[i] == 1)
			{
				ans = i;
				break;
			}
			else
				continue;
		}
	cout << ans;
	return 0;
}