#include <iostream>
#include <fstream>
#include <vector>
#include <stack>

using namespace std;

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

int N,M,i,x,y;
vector<int> G[100001],ANS;
pair<int,int> Edge[500001];
int visited[5000001];

void ciclueuler()
{
    int x, edge = 1;
    stack<int> Stack;

    Stack.push(1);
    while (!Stack.empty())
    {
        edge=Stack.top();
        if (G[edge].empty())
        {
            ANS.push_back(edge);
            Stack.pop();

        }
        else
        {
            x=G[edge].back();
            G[edge].pop_back();
            if (visited[x] == 0)
            {
                visited[x] = 1;
                Stack.push(Edge[x].first^Edge[x].second^edge);
            }
        }
    }
}
int main()
{
    in>>N>>M;
    for (int i=1; i<=M; i++)
    {
        in>>x>>y;
        G[x].push_back(i);
        G[y].push_back(i);
        Edge[i] = make_pair(x,y);
    }

    for (int i=1; i<=N; i++)
        if (G[i].size()%2 ==  1)
        {
            out<<"-1\n";
            return 0;
        }

    ciclueuler();
    ANS.pop_back();
    for (i = 0; i < ANS.size(); i++)
        out<<ANS[i]<<' ';

    return 0;

}