#include<bits/stdc++.h> using namespace std; int father[1001]; int find(int x) { if (father[x]!=x) father[x]=find(father[x]); return father[x]; } void hebin(int a,int b){ int faA=find(a); int faB=find(b); if(faA!=faB){ father[faB]=faA; } } int main() { int n,m; int a,b; while(cin>>n>>m) { if(n==0&&m==0)return 0; for(int i=1;i<=n;i++)father[i]=i; for(int i=1;i<=m;i++){ cin>>a>>b; hebin(a,b); } if(m+1>n)cout<<"No"<<endl; int i; for(i=1;i<n;i++){ if(father[i]!=father[i+1]) break; } if(i==n)cout<<"Yes"<<endl; else cout<<"No"<<endl; } return 0; }