#include<fstream>
#include<algorithm>
#include<vector>
using namespace std;
ifstream fin("ciclueuler.in");
ofstream fout("ciclueuler.out");
int x,y,ajung[100001],i,OK,n,m;
vector<int> v[100001];
int main()
{
	fin>>n>>m;
	for(i=1;i<=m;i++)
	{
		fin>>x>>y;
		v[x].push_back(y);
		ajung[x]++;ajung[y]++;
		v[y].push_back(x);
	}
	for(i=1;i<=n;i++)
	{
		if(ajung[i]%2==1)
		{
			fout<<-1;
			OK=1;
			break;
		}
	}
	return 0;
}