uva539

//直接回溯

#include<stdio.h>  #include<string.h>#include<ctype.h>#include<stdlib.h>#include<math.h>int n,m,minn;int a[50][50],vis[50][50];void dfs(int x,int sum){int i;if(sum>minn)minn=sum;for(i=0;i<n;i++){if(a[x][i]&&!vis[x][i]){vis[i][x]=vis[x][i]=1;dfs(i,sum+1);vis[i][x]=vis[x][i]=0;}}}main(){int i,u,v;//freopen("D:\\in.txt","r",stdin);while(scanf("%d%d",&n,&m)&&n+m){memset(a,0,sizeof(a));memset(vis,0,sizeof(vis));for(i=0;i<m;i++){scanf("%d%d",&u,&v);a[u][v]=a[v][u]=1;}minn=0;for(i=0;i<n;i++)dfs(i,0);printf("%d\n",minn);}return 0;}