#include <bits/stdc++.h>
using namespace std;
ifstream fin("ciclueuler.in");
ofstream fout("ciclueuler.out");
vector <int> v[100005];
int n,m,x,y;
bool g[100005],viz[100005];
/*bool Grad()
{
    for(int i=1;i<=n;++i)
        if(g[i])return 1;
    return 0;
}*/
void Read()
{
    fin>>n>>m;
    for(int i=1;i<=m;++i)
    {
        fin>>x>>y;
        if(g[x]==0)g[x]=1;
        else g[x]=0;
        if(g[y]==0)g[y]=1;
        else g[y]=0;
        v[x].push_back(y);
        v[y].push_back(x);
    }
    for(int i=1;i<=n;++i)
        if(g[i]){fout<<-1;return;}
}
int main()
{
   Read();
    return 0;
}