#include<cstdio>#include<cstring>#include<algorithm>using namespace std;struct Edge{ int a,b,next;}edge[100];int head[100],nc,ans,pos;bool mark[100];void add(int a,int b){ edge[nc].a=a;edge[nc].b=b;edge[nc].next=head[a];head[a]=nc++;}void dfs(int now,int len){ if(len>ans) ans=len,pos=now; for(int i=head[now];i!=-1;i=edge[i].next) { if(mark[i>>1]) continue; int t=i>>1; mark[t]=true; dfs(edge[i].b,len+1); mark[t]=false; }}int main(){ int n,m,a,b; while(scanf("%d%d",&n,&m),n||m) { nc=ans=pos=0; memset(head,-1,sizeof(head)); for(int i=0;i<m;i++) { scanf("%d%d",&a,&b); add(a,b);add(b,a); } memset(mark,false,sizeof(mark)); dfs(0,0); dfs(pos,0); printf("%dn",ans); } return 0;}
