#include<iostream>
#include<cstring>
#include<vector>
using namespace std;
const int N = 1010;
vector<int> q[N];
int n,m;
bool st[N];

void inputData()
{
    memset(q,0,sizeof q);
    memset(st, false, sizeof st);
    for(int i=0;i<m;i++)
    {
        int a,b;
        cin>>a>>b;
        q[a].push_back(b);
        q[b].push_back(a);
    }
}

void dfs(int u)
{
    st[u] = true;

    for(auto t : q[u])
        if(!st[t])
            dfs(t);
}

bool judge_dfs()
{
    inputData();

    bool flag = true;
    dfs(1);
    for(int i=1;i<=n;i++)
    {
        if(!st[i])
        {
            flag = false;
            break;
        }
    }
    return flag;
}

bool judge_bfs()
{
    inputData();

    st[1] = true;
    int que[N];
    int hh = 0, tt = -1;
    que[++tt] = 1;
    while(hh <= tt)
    {
        int t = que[hh++];
        for(auto i : q[t])
            if(!st[i])
            {
                que[++tt] = i;
                st[i] = true;
            }
    }

    return hh == n;
}


int p[N];
int find(int x)
{
    if(p[x] != x) p[x] = find(p[x]);
    return p[x];
}


bool judge_union_find()
{
    memset(p,0,sizeof p);

    for(int i=1;i<=n;i++)   p[i] = i;

    for(int i=1;i<=m;i++)
    {
        int a,b;
        cin>>a>>b;
        int pa = find(a), pb = find(b);
        if(pa != pb)
            p[pa] = pb;
    }

    int r = find(1);
    bool flag = true;
    for(int i=1;i<=n;i++)
        if(find(i) != r)
        {
            flag = false;
            break;
        }
    return flag;
}


int main()
{
    while(cin>>n>>m)
    {
        if(judge_union_find()) cout<<"YES"<<endl;
        else cout<<"NO"<<endl;
    }  
}