#include<stdio.h>

#include<iostream>

#include<vector>

using namespace std;

const int maxn=;

vector<int>g[maxn];

int Bcnt;

int Top;

int Index;

int low[maxn],dfn[maxn];

int belong[maxn],stack[maxn];

int instack[maxn];

void Init_tarjan(int n)

{

    Bcnt=Top=Index=;

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

        low[i]=dfn[i]=;

}

void Tarjan(int u)

{

    stack[Top++]=u;

    instack[u]=;

    low[u]=dfn[u]=++Index;

    for(int i=;i<g[u].size();i++)

    {

        int v=g[u][i];

        if(!dfn[v])

        {

            Tarjan(v);

            low[u]=min(low[v],low[u]);

        }

        else

        {

            if(instack[v])

                low[u]=min(low[u],dfn[v]);

        }

    }

    if(low[u]==dfn[u])

    {

        ++Bcnt;

        int v;

        do

        {

            v=stack[--Top];

            instack[v]=;

            belong[v]=Bcnt;

        }

        while(u!=v);

    }

}

int main()

{

    int n,m;

    int i;

    int x,y;

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

    {

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

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

            g[i].clear();

        while(m--)

        {

            scanf("%d %d",&x,&y);

            g[x].push_back(y);

        }

        Init_tarjan(n);

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

        {

            if(!dfn[i])

                Tarjan();

        }

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

        else printf("No\n");

    }

    return ;

}