#include <fstream>
#include <vector>
#define NMAX 100002
#define MMAX 500002
using namespace std;
ifstream  fin("ciclueuler.in");
ofstream fout("ciclueuler.out");
int N,M;
vector<int> graph[NMAX],grad(NMAX);

void citire()
{
    fin>>N>>M;

    int u,v;
    for(int i=1; i<=M; i++)
    {
        fin>>u>>v;
        graph[u].push_back(v);
        graph[v].push_back(u);
        grad[u]++;
        grad[v]++;
    }
}

int main()
{
    citire();

    for(int i=1; i<=N; i++)
    {
        if(grad[i]%2==1)
        {
            fout<< -1 << "\n";
            return 0;
        }
    }


    return 0;
}