#include <iostream>
#include <vector>
using namespace std;
const int N=3e5+7;
int n, m;
vector<int> e[N];
int dp[N], frm[N], fa[N];
void dfs(int x, int f){
	fa[x]=f;
	dp[x]=1;
	for(int i=0;i<e[x].size();i++){
		if(e[x][i]!=f){
			dfs(e[x][i], x);
			if(dp[e[x][i]]+e[x].size()-1>dp[x]){
				dp[x]=dp[e[x][i]]+e[x].size()-(f>0);
				frm[x]=e[x][i];
			}
		}
	}
}
int main(){
	cin>>n>>m;
	while(m--){
		int x, y;
		cin>>x>>y;
		e[x].push_back(y);
		e[y].push_back(x);
	}
	dfs(1, 0);
	int ans=0;
	for(int i=1;i<=n;i++)
		for(int j=0;j<e[i].size();j++)
			if(e[i][j]!=fa[i] && e[i][j]!=frm[i])
				ans=max(ans, dp[i]+dp[e[i][j]]-1);
	cout<<ans<<endl;
	return 0;
}