#include <cstdio>

#include <cmath>

#include <algorithm>

#include <iostream>

#include <cstdlib>

#include <string>

#include <queue>

#include <stack>

#include <cstring>

#define CL(a,b) memset(a,b,sizeof(a))

#define ll __int64

#define TEST cout<<"TEST   ***"<<endl;

#define INF 0x7ffffff0

#define MOD 1000000007

using namespace std;

typedef struct myedge

{

    int e,next;

}E;

E edge[];

stack <int> st;

int head[],ct,tim;

int ti[],lo[],ins[],n,m;

void inithead()

{

    CL(head,-);

    tim=;

    ct=;

}

void addedge(int s,int e)

{

    edge[ct].e=e;edge[ct].next=head[s];head[s]=ct++;

}

void targan(int i)

{

    tim++;

    ti[i]=tim;lo[i]=tim;

    st.push(i);

    ins[i]=;

    int p=head[i];

    int v;

    while(p!=-)

    {

        v=edge[p].e;

        if(ins[v]==)

        {

            lo[i]=min(lo[v],lo[i]);

        }

        else if(ti[v]==)

        {

            targan(v);

            lo[i]=min(lo[i],lo[v]);

        }

        p=edge[p].next;

    }

    if(lo[i]==ti[i])

    {

        while(!st.empty()&&lo[st.top()]==ti[i])

        {

            ins[st.top()]=;

            st.pop();

        }

    }

}

int main()

{

    while(scanf("%d %d",&n,&m)!=EOF)

    {

        if(n==&&m==)break;

        int i,j,a,b;

        inithead();

        CL(lo,);

        CL(ti,);

        CL(ins,);

        for(i=;i<m;i++)

        {

            scanf("%d %d",&a,&b);

            addedge(a,b);

        }

        targan();

        int re=;

        for(i=;i<=n;i++)

        {

            if(lo[i]==ti[i])re++;

        }

  //      cout<<re<<endl;

        if(re==)printf("Yes\n");

        else printf("No\n");

    }

    return ;

}