#include <bits/stdc++.h>
#define vi vector<int>
#define int long long
#define pb push_back
#define all(x) (x).begin(), (x).end()
using namespace std;
const int N = 1e3+5;
vi graf[N];
int njgl=0;
int naj=0;
void dfs(int u, int p=-1, int gl=0)
{
if (gl>njgl)
naj=u, njgl=gl;
for (int v:graf[u])
if (v!=p)
dfs(v, u, gl+1);
}
bool mz=1;
int preveri(int u, int p=-1)
{
int sm = 0; vi o;
for (int v:graf[u])
if (v!=p)
o.pb(preveri(v, u));
sort(all(o));
if (o.size()>1 && o[0]>=2)
mz=0;
if (o.size())
sm=o.back();
return sm+1;
}
signed main()
{
int n, m;
cin >> n >> m;
for (int i = 0; i < m; i++)
{
int u, v;
cin >> u >> v;
graf[u].pb(v);graf[v].pb(u);
}
if (m!=n-1)
{
cout << "NO\n";
return 0;
}
dfs(0);
njgl=0;
dfs(naj);
int t = preveri(naj);
if (mz)
cout << "YES\n1\n1\n";
else
cout << "NO\n";
return 0;
}
