#include<bits/stdc++.h>
using namespace std;

const long long MaxN = 1e5 + 5;

long long n, m;
vector<long long> a[MaxN];
bool visited[MaxN];

void input()
{
    cin >> n >> m;

    for (long long i = 1; i <= m; i++)
    {
        long long u, v;
        cin >> u >> v;

        a[u].push_back(v);
        a[v].push_back(u);
    }
}

void dfs(long long s)
{
    stack<long long> st;

    st.push(s);
    visited[s] = true;

    while (!st.empty())
    {
        long long u = st.top();
        st.pop();

        for (long long v : a[u])
        {
            if (!visited[v])
            {
                visited[v] = true;
                st.push(v);
            }
        }
    }
}

void solve()
{
    if (m != n - 1)
    {
        cout << "NO";
        return;
    }

    dfs(1);

    for (long long i = 1; i <= n; i++)
    {
        if (!visited[i])
        {
            cout << "NO";
            return;
        }
    }

    cout << "YES";
}

int main()
{
    input();
    solve();
}