#include <cstdio>
#include <vector>
#include <queue>
#include <stack>
#define Nmax 100010
#define pb push_back
using namespace std;

int n,m1,grad[Nmax],viz[Nmax];
vector<int>::iterator it;
vector<int> m[Nmax];
queue<int> c;

int is_eulerian()
{
    int okgrad=1,i,nrvf=0,nod;
    c.push(1); viz[1]=1; nrvf=1; if(grad[1]%2==1) okgrad=0;
    if(okgrad==0) return 0;
    else
    {
        while(!c.empty())
        {
            nod=c.front(); c.pop();
            for(it=m[nod].begin();it!=m[nod].end();it++)
            {
                if(grad[*it]%2==1) { okgrad=0; return 0; }
                if(!viz[*it]) { c.push(*it); nrvf++; viz[*it]=1; }
            }
        }
        if(nrvf==n) return 1;
               else return 0;
    }

}

int main()
{
    freopen("ciclu.in","r",stdin);
    freopen("ciclu.out","w",stdout);

    int n1,n2,i;
    scanf("%d%d",&n,&m1);
    for(;m1;m1--)
    {
        scanf("%d%d",&n1,&n2);
        m[n1].pb(n2);
        m[n2].pb(n1);
        grad[n1]++; grad[n2]++;
    }

    if(!is_eulerian()) printf("-1\n");
    else
    {

    }
    fclose(stdin);
    fclose(stdout);
    return 0;
}