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

ifstream f ("ciclueuler.in");
ofstream g ("ciclueuler.out");

const int NMAX = 100000;
int n, m;

struct muchie {
    int x, y;
};

vector<int> G[NMAX+1], L;
vector<muchie> M;
vector<bool> elim;
stack<int> S;


void citire() {
    int x, y;
    f >> n >> m;
    while(m--) {
        f >> x >> y;
        M.push_back({x, y});
        elim.push_back(0);
        G[x].push_back(M.size()-1);
        G[y].push_back(M.size()-1);
    }
}

void euler() {
    int v, p, k;
    S.push(1);
    while(!S.empty()) {
        v = S.top();
        if(G[v].size() > 0) {
            k = G[v].back();
            G[v].pop_back();
            if(!elim[k]) {
                elim[k] = 1;
                p = M[k].y;
                if (p == v) p = M[k].x;
                S.push(p);
            }
        } else {
            L.push_back(v);
            S.pop();
        }
    }
}

int main()
{
    bool ok = 1;
    citire();
    for (int i=1; i<=n && ok; i++)
        if(G[i].size() & 1)
            ok = 0;
    if(ok) {
        euler();
        for(int i=L.size()-1; i>=1; i--)
            g << L[i] << ' ';
    } else
        g << "-1\n";
    f.close();
    g.close();
    return 0;
}