#include <stdio.h>#include <string.h>#define MAXN 1001class DisjointSet{public:DisjointSet(){}void Make_Set(int s){size = s;for(int i = 0;i < s; i++){parent[i] = -1;}}int Find_Set(int i){int j, k, t;for(j = k = i; parent[j] >= 0; j = parent[j]);while(k != j){t = parent[k];parent[k] = j;k = t;}return j;}void Union(int x, int y){if(x == y)return;int root_x = Find_Set(x);int root_y = Find_Set(y);if(root_x == root_y)return; if(parent[root_x] < parent[root_y]){parent[root_x] += parent[root_y];parent[root_y] = root_x;}else{parent[root_y] += parent[root_x];parent[root_x] = root_y;}}protected:int parent[MAXN];//int rank[MAXN];int size;};int main(int argc,char **argv){int N,M,i,a,b,x,y;bool duplicated = false;int flag[MAXN]; DisjointSet ds;while(true){scanf("%d %d",&N, &M);if(N==0 && M ==0)break;ds.Make_Set(N);duplicated = false;for(i = 0; i < M; i++){scanf("%d %d",&a, &b);x = ds.Find_Set(a-1);y = ds.Find_Set(b-1);if(x == y)duplicated = true;ds.Union(x,y);flag[a-1] = flag[b-1] = 1;}int v = 0;for(i=0; i< N; i++)v += flag[i];if(v == N && v == M+1 && !duplicated){printf("Yesn");}else{printf("Non");}}return 0;}
