#include<bits/stdc++.h>
using namespace std;
const int maxn = 1e3 + 10;
vector <int> adj[maxn];
bool mark[maxn];
bool mar[maxn];
int par[maxn];
bool cycle = false;
void dfs(int u){
    mark[u] = true;
    for(auto v: adj[u]){
        if(!mark[v]){
            par[v] = u;
            dfs(v);
        }
        else{
            if(v != par[u]){
                cycle = true;
            }
        }
    }
}
int main(){
    ios_base::sync_with_stdio(false); cin.tie(NULL); cout.tie(NULL);
    int n, m; cin >> n >> m;
    for(int i = 0; i < m; i ++){
        int u, v;
        cin >> u >> v;
        u --; v --;
        adj[u].push_back(v);
        adj[v].push_back(u);
    }
    dfs(0);
    int x = 0;
    for(int i = 0; i < n; i ++){
        if(adj[i].size() == 1){
            x = i;
        }
    }
    if(cycle){
        cout << "NO";
    }
    else{
        cout << "YES" << endl;
        
        cout << 4 * n + 1 << endl;
        for(int i = 1; i <= n; i ++){
            cout << i << " " << i << " ";
        }
        cout << n << " ";
        for(int i = 1; i <= n; i ++){
            cout << i << " " << i << " ";
        }  
    }
    return 0;
}
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