/******************************************************************************

                              Online C++ Compiler.
               Code, Compile, Run and Debug C++ program online.
Write your code in this editor and press "Run" button to compile and execute it.

*******************************************************************************/

#include <iostream>
#include <vector>
#include <queue>
using namespace std;



struct nodus{
    int nod,poz;
    bool viz;
}

vector<nodus> graf_muchii[100001];

bool conex()
{
    bool viz[100001]={0};
    int nodviz;
    queue<int> que;
    que.push(1);
    v[1]=1;
    
    while(!que.empty())
    {
        int nod=que.front();
        que.pop();
        
        for(int vecin:graf_muchii[nod])
        {
            que.push(vecin)
            if(!viz[vecin])
            {
                nodviz++;
                viz[vecin]=1;
            }
            
        }
        
        
    }
}

int main()
{
    cin>>n>>m;
    for(i=1;i<=;i++)
    {nodus crt;
    
    cin>>x>>y;
    
    crt.nod=y;
    crt.poz=garf_muchii[y].size();
    
    if(x==y)
    crt.poz++;
    
    graf_muchii[x].push_back(crt);
    
    crt.nod=x;
    crt.poz=graf_muchii[x].size()-1;
    
    graf_muchii[y].push_back(crt);
    
     if(!conex())
     {cout<<-1;
     return 0;
     }
     else if(prea_mult_impar()==1)
     {
         cout<<-1;
         return 0;
     }
        
        
    }

    return 0;
}