#include <iostream>
#include <vector>
#include <cmath>
using namespace std;

struct Rebra
{
	int one;
	int two;
	bool check;
};
void way(vector<Rebra> &s, )
{

}
int main()
{
	int n, m,summ(0);
	cin >> n >> m;
	vector<int> Ch (n+1);
	vector<Rebra> s(m);
	for (int i(0); i < m;i++)
	{
		cin >> s[i].one >> s[i].two;
		Ch[s[i].one]++;
		Ch[s[i].two]++;
	}
	for (int i(1);i<=n;i++)
		if (Ch[i]%2 != 0)
			summ++;
	if (summ != 2 || summ !=0)
		{
			cout << -1 << endl;
			return 0;
		}
	for (int i(0);i < m;i++)
		if (Ch[i]%2 == 1)



return 0;
}