#include<cstdio>#include<cstring>#include<iostream>#include<queue>using namespace std;const int inf=1<<29;const int maxn=510;const int maxm=5e4;int e,dfscolck,head[maxn],pnt[maxm],nxt[maxm],dfn[maxn],low[maxn];int n,m,root;bool lost[maxn];void AddEdge(int u,int v){ pnt[e]=v;nxt[e]=head[u];head[u]=e++;}int DFS(int u,int f,bool &find){ dfn[u]=low[u]=++dfscolck; int child=0; for(int i=head[u];i!=-1;i=nxt[i]) { if(lost[pnt[i]]) continue; if(!dfn[pnt[i]]) { child++; low[u]=min(low[u],DFS(pnt[i],u,find)); if(find) return low[u]; if(u==root&&child>1||u!=root&&low[pnt[i]]>=dfn[u]) { find=true; return low[u]; } } else if(dfn[pnt[i]]<dfn[u]&&pnt[i]!=f) { low[u]=min(low[u],dfn[pnt[i]]); } } return low[u];}void solve(){ bool is=false; for(int i=0;i<n;i++) { lost[i]=1; dfscolck=0; memset(dfn,0,sizeof(dfn)); root=(i+1)%n; DFS(root,-1,is); for(int j=0;j<n;j++) if(j!=i&&!dfn[j]) { is=true; break; } lost[i]=0; if(is) break; } if(is) printf("NOn"); else printf("YESn");}int main(){ while(scanf("%d%d",&n,&m)&&(n+m)) { e=0; memset(head,-1,sizeof(head)); for(int i=0;i<m;i++) { int u,v; scanf("%d%d",&u,&v); AddEdge(u,v); AddEdge(v,u); } if(n<=2) { printf("NOn"); continue; } solve(); } return 0;}
