#include <bits/stdc++.h>
using namespace std;
#define cin fin
#define cout fout
ifstream cin("ciclueuler.in");
ofstream cout("ciclueuler.out");

int v[100005];
vector<vector<int>>vec;
map<pair<int,int>,int>mp;
int n,m;

int main()
{
   cin>>n>>m;
   vec.resize(n+1);
   for(int i=0;i<m;i++)
   {
       int a,b;
       cin>>a>>b;
       v[a]++;
       v[b]++;
       mp[{a,b}]++;
       mp[{b,a}]++;
    vec[a].push_back(b);
       vec[b].push_back(a);
   }
   int cnt=0;
   int y=0;
   for(int i=1;i<=n;i++)
   {
       if(v[i]%2==1)
       {
           cnt++;
           y=i;
       }
   }
   if(cnt>1)
    cout<<-1;

    return 0;
}