#include<iostream>
#include<cstdio>
#include<cmath>
#include<string>
#include<queue>
#include<algorithm>
#include<stack>
#include<cstring>
#include<vector>
#include<list>
#include<set>
#include<map>
using namespace std;
#define ll __int64
#define inf 2000000001
int scan()
{
    int res = 0 , ch ;
    while( !( ( ch = getchar() ) >= ‘0‘ && ch <= ‘9‘ ) )
    {
        if( ch == EOF )  return 1 << 30 ;
    }
    res = ch - ‘0‘ ;
    while( ( ch = getchar() ) >= ‘0‘ && ch <= ‘9‘ )
        res = res * 10 + ( ch - ‘0‘ ) ;
    return res ;
}
struct is
{
    int u,v;
    int next;
}edge1[100010],edge2[100010];
int flag1[10010],flag2[10010];
int jiedge1,jiedge2;
int jidian1,jidian2;
int head1[100010],head2[100010];
int shun1[100010],shun2[100010];
int belong[100010];
int n,m;
void update(int x,int y)
{
    jiedge1++;
    edge1[jiedge1].u=x;
    edge1[jiedge1].v=y;
    edge1[jiedge1].next=head1[x];
    head1[x]=jiedge1;
    jiedge2++;
    edge2[jiedge2].u=y;
    edge2[jiedge2].v=x;
    edge2[jiedge2].next=head2[x];
    head2[x]=jiedge2;
}
void dfs1(int x)
{
    flag1[x]=1;
    for(int i=head1[x];i;i=edge1[i].next)
    {
        if(!flag1[edge1[i].u])
        dfs1(edge1[i].u);
    }
    shun1[++jidian1]=x;
}
void dfs2(int x)
{
    flag2[x]=1;
    belong[x]=jidian2;
    for(int i=head2[x];i;i=edge2[i].next)
    {
        if(!flag2[edge2[i].u])
        dfs2(edge2[i].u);
    }
}
void Kosaraju()
{
    memset(flag1,0,sizeof(flag1));
    memset(flag2,0,sizeof(flag2));
    jidian1=0;
    for(int i=1;i<=n;i++)
    if(!flag1[i])
    dfs1(i);
    jidian2=1;
    for(int i=jidian1;i>0;i--)
    {
        if(!flag2[i])
        {
            dfs2(shun1[i]);
            jidian2++;
        }
    }
}
int main()
{
    int i;
    while(~scanf("%d%d",&n,&m))
    {
        memset(head1,0,sizeof(head1));
        memset(head2,0,sizeof(head2));
        if(n==0&&m==0)break;
        jiedge1=0;
        jiedge2=0;
        for(i=1;i<=m;i++)
        {
            int u,v;
            scanf("%d%d",&u,&v);
            update(u,v);
        }
        Kosaraju();
        /*for(i=1;i<=n;i++)
        cout<<belong[i]<<" ";
        cout<<endl;*/
        int lu=0,ans=belong[1];
        for(i=2;i<=n;i++)
        if(belong[i]!=ans)
        {
            lu=1;
            break;
        }
        if(lu)
            printf("No\n");
        else
            printf("Yes\n");
    }
    return 0;
}