#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;
        }
    }
    cout<<-1;

    return 0;
}