#include <bits/stdc++.h>
#define int long long
#define pb push_back
bool debug=1;

#define dbg(x) if(debug)cerr <<  #x <<  " = " << (x) <<endl
using namespace std;void ass(string err){cout<<err<<"\n";exit(0);}void ass(int err){cout<<err<<"\n";exit(0);}
typedef pair < long double,long double> pii;
const string COLOR_RESET = "\033[0m",  BRIGHT_CYAN = "\033[1;36m", NORMAL_FAINT = "\033[0;2m";

const int maxn=200050;
int par[maxn][22];
int dep[maxn];
int vis[maxn];
int C=19;
vector<int>  a[maxn];
void dfs(int u,int pre)  //���ڵ����Ϊ1 
{
	dep[u]=dep[pre]+1;
	par[u][0]=pre;
	vis[u] = 1;
	for(int i=1;i<C;i++)
	{
		par[u][i]=par[par[u][i-1]][i-1];
	}
	for(auto p:a[u])
	{
		if(vis[p]==0)
		dfs(p,u);
	}
}
int lca(int x,int y)
{
	if(dep[y]>dep[x])swap(x,y);
	
	for(int i=C-1;i>=0;i--)
	{
		if(dep[par[x][i]]>=dep[y])
		x=par[x][i];
	}
	if(x==y)return y;
	for(int i=C-1;i>=0;i--)
	if(par[x][i]!=par[y][i])
	{
		x=par[x][i];
		y=par[y][i];
	}
	return par[x][0];
}
int getfa(int u,int k){//����k�� 
	int res=u;
	for(int i=C-1;i>=0;i--){
		if(k&(1ll<<i)){
			res=par[res][i];
		}
	}
	return res;
}
int dis(int u,int v){
	return dep[u] + dep[v] - dep[lca(u, v)] * 2;
}
void solve()
{
	ios::sync_with_stdio(false);cin.tie(0);mt19937_64 engie(202202052100238523);
	int n, m;
	cin>>n>>m;
	for (int i = 0; i < m;i++){
		int u, v;cin>>u>>v;
		a[u].pb(v);
		a[v].pb(u);
	}
	dfs(1, 0);
	int ans = 3;
	for (int i = 1; i <= n * 2;i++)
	 for(auto p:a[i]){
		if(dis(i,p)==3)
			ans = 2;
	 }
	cout << ans;
}

signed main()
{
	ios::sync_with_stdio(false);
	cin.tie(0);
	cout.tie(0);
	//freopen("input.txt","r",stdin);
    //freopen("output.txt","w",stdout);
	int t=1;
//	cin>>t;
	while(t--)
	{
		solve();
		cout <<'\n';
	}
	return 0;
}

//__builtin_popcountl( ) 计算二进制1个数
//cout<<fixed<<setprecision(2);输出小数，四舍六入五取偶 
//__builtin_ctz( )返回末尾0的个数
//__builtin_clz( ) 返回前导0的个数
//__builtin_parity( )返回1的个数的奇偶性，偶数返回0
//__builtin_ffs( )返回最后一个1在第几位
//__builtin_sqrt( )快速开平方 
//stoll()字符串转为长整形
//点(x,y)的极角atan2(y,x)
//点(x,y)逆时针旋转A度，(x*cosA-y*sinA ,  x*sinA+y*cosA ) 
//C(n,k)+C(n,k-1)=(n+1,k)
//string s(str,stridx,strlen) //将字符串str内“始于stridx且长度顶多strlen”
//（从stridx开始往后strlen个字符）的部分作为字符串的初值
/*

*/