#include <cstdio>
#include <cstdlib>
#include <stack>
#include <vector>
using namespace std;

const int NMAX = 100010;

int N, M, X, Y, Ans[5 * NMAX];
bool Out[5 * NMAX];
vector<pair<int, int> > G[NMAX];
stack<int> S;

void Euler()
{
    S.push(1);
    while(!S.empty())
    {
        int Node = S.top();
        while(!G[Node].empty() && Out[ G[Node].back().second ]) G[Node].pop_back();
        if(G[Node].size())
        {
            int Son = G[Node].back().first, Index = G[Node].back().second;
            Out[Index] = 1;
            S.push(Son);
        }else
        {
            Ans[++Ans[0]] = Node;
            S.pop();
        }
    }
}

int main()
{
    freopen("ciclueuler.in", "r", stdin);
    freopen("ciclueuler.out", "w", stdout);

    scanf("%i %i", &N, &M);
    for(int i = 1; i <= M; ++ i)
    {
        scanf("%i %i", &X, &Y);
        G[X].push_back(make_pair(Y, i));
        G[Y].push_back(make_pair(X, i));
    }

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

    Euler();

    for(int i = 1; i < Ans[0]; ++ i)
        printf("%i ", Ans[i]);
}