TOURISTS

#include"bits/stdc++.h"
using namespace std;
#define mp make_pair
#define pb push_back
vector< pair<int,int> > original;
set<int> adj[100005];
set< pair<int,int> > tour;
void dfs(int v, bool visited[])
{
    visited[v] = true;

    set<int>::iterator i;
    for (i = adj[v].begin(); i != adj[v].end(); ++i)
        if (!visited[*i])
            dfs(*i, visited);
}
void findtour(int u)
{
    while(!adj[u].empty())
    {
        set<int>::iterator it=adj[u].begin();
        int e=*it;
        adj[u].erase(e);
        adj[e].erase(u);
        tour.insert(mp(u,e));
        findtour(e);
    }


}
int main()
{
    int n,e;
        bool ok=true;
    scanf("%d%d",&n,&e);
    int i,j;
    int freq[100005]={0};
    original.clear();
    //adj.clear();
    for(i=0;i<e;i++)
    {
        int u,v;
        scanf("%d%d",&u,&v);
        original.pb(mp(u,v));
        freq[u]+=2;
        freq[v]+=2;
        adj[u].insert(v);
        adj[v].insert(u);
    }
    /*check for degrees*/
    for(i=0;i<n+1;i++)
    {
        if((freq[i]/2)&1)
        ok=false;
    }
    /*check for connected graph*/
    bool visited[n+1];
  //  int i;
    for (i = 0; i < n+1; i++)
        visited[i] = false;
    for (i = 1; i < n+1; i++)
        if (adj[i].size() != 0)
            break;
    dfs(i,visited);
    for (i = 1; i < n+1; i++)
       if (visited[i] == false && adj[i].size() > 0)
            ok=false;
    if(!ok)
    {
        cout<<"NO"<<endl;
    }
    else
    {
        findtour(1);
        cout<<"YES"<<endl;
        for(vector< pair<int,int> >::iterator it=original.begin();it!=original.end();it++)
        {
            if(tour.find(mp(it->first,it->second))!=tour.end())
            cout<<it->first<<" "<<it->second<<endl;
            else
            cout<<it->second<<" "<<it->first<<endl;
            //cout<<it->first<<" "<<it->second<<endl;
        }
    }
}