#include <iostream>
#include <fstream>
#include <algorithm>
#include <vector>
#include <bitset>
#include <stack>
using namespace std;

#define MAXN 100010
#define MAXM 500010
typedef vector< pair<int, int> >::iterator iter;

FILE *f = fopen("ciclueuler.in", "r");
FILE *g = fopen("ciclueuler.out", "w");

int n, m;
vector< pair<int, int> > G[MAXN];
bitset<MAXM> vizmuchie;
vector<int> sol;
int grd[MAXN];
stack<int> stiva;

bool iseuler() {
    for (int i = 1; i <= n; i++) {
        if (grd[i] & 1 == 1) {
            return false;
        }
    }
    return true;
}

void euler() {
    stiva.push(1);
    while (!stiva.empty()) {
        int nd = stiva.top();

        if (!G[nd].empty()) {
            stiva.push(G[nd][0].first);
            G[G[nd][0].first].erase(find(G[G[nd][0].first].begin(), G[G[nd][0].first].end(), make_pair(nd, G[nd][0].second)));
            G[nd].erase(G[nd].begin());
            continue;
        }

        sol.push_back(nd);
        stiva.pop();
    }
}

int main()
{
    fscanf(f, "%d %d\n", &n, &m);
    for (int i = 1; i <= m; i++) {
        int x, y;
        fscanf(f, "%d %d\n", &x, &y);

        G[x].push_back(make_pair(y, i));
        G[y].push_back(make_pair(x, i));

        grd[x] ++;
        grd[y] ++;
    }

    if (iseuler() == true) {
        vizmuchie.reset();
        euler();
        for (int i = 0; i < sol.size() - 1; i++) {
            fprintf(g, "%d ", sol[i]);
        }
    } else {
        fprintf(g, "-1");
    }

    fclose(f);
    fclose(g);
    return 0;
}