#include <bits/stdc++.h>
using namespace std;
ifstream f("ciclueuler.in");
ofstream g("ciclueuler.out");
const int NMAX = 100005, MMAX = 500005;
vector<int> G[NMAX];
bool vizitat[MMAX];
int from[MMAX], to[MMAX];
int main() {

    int n, m;
    f>> n >> m;
    for (int i = 1; i <= m; i++) {
        int x, y;
        f>> x >> y;
        G[x].push_back(i);
        G[y].push_back(i);
        from[i] = x;
        to[i] = y;
    }

    for (int i = 1; i <= n; ++i) {
        if (SZ(G[i]) & 1) {
            g << "-1\n";
            return 0;
        }
    }

   // for (int i = 0; i < SZ(ans) - 1; ++i) {
      //  g << ans[i] << ' ';

    g << '\n';

   return 0;
}