using namespace std;
#include<iostream>
#include<fstream>
#include<vector>
#include<stack>
#define NMAX 100002
#define MMAX 500002

ifstream fin("ciclueuler.in");
ofstream fout("ciclueuler.out");

struct varf{int x, nr;};
int n,m,start;
vector<varf> G[NMAX];
bool uz[NMAX];
int d[NMAX];
int eulerian;
stack<int> S;
void citire();
int grade_pare();
void euler(int start);

int main() {
    citire();

    if (!(start = grade_pare())) {
        fout << "-1\n";
    } else {
        euler(start);
        eulerian = 1;
        for (int i = 1; i<=m; i++) {
            if (!uz[i]) {
                eulerian = 0;
            }
        }
        if (!eulerian) {
            fout.close();
            fout.open("ciclueuler.out");
            fout << "-1\n";
        }
    }

    fout.close();

    return 0;
}

void citire() {
    varf vf;
    fin >> n >> m;
    for (int i = 1; i<=m; i++) {
        int x,y;
        fin >> x >> y;
        vf.x = y, vf.nr = i;
        G[x].push_back(vf);
        vf.x = x, vf.nr = i;
        G[y].push_back(vf);
        d[x]++, d[y]++;
    }
}
int grade_pare() {
    for (int i = 1; i<=n; i++) {
        if (d[i]%2) return 0;
        if (d[i]) start = i;
    }
    return start;
}

void euler(int start) {
    varf vfad;
    S.push(start);
    int vf;
    while (!S.empty()) {
        vf = S.top();
        if (!G[vf].empty()) {
            vfad = G[vf][G[vf].size()-1];
            if (!uz[vfad.nr]) {
                uz[vfad.nr] = 1;
                S.push(vfad.x);
            }
            G[vf].pop_back();
        } else {
            fout << ' ' << vf;
            S.pop();
        }
    }
}