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

const int NMAX = 100010;

int N, M, A, B, Deg[NMAX];
vector<pair<int, int> > G[NMAX];
vector<int> Order;
bool Used[NMAX];
stack<int> S;

void Euler()
{
    S.push(1);
    while(!S.empty())
    {
        int Node = S.top();
        while(G[Node].size() && Used[ G[Node].back().second ]) G[Node].pop_back();

        if(G[Node].empty()) Order.push_back(Node), S.pop();
        else
        {
            int Vec = G[Node].back().first, Ind = G[Node].back().second;
            Used[Ind] = 1;
            G[Node].pop_back();
            S.push(Vec);
        }
    }
}

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", &A, &B);
        G[A].push_back(make_pair(B, i));
        G[B].push_back(make_pair(A, i));
        Deg[A] ++;
        Deg[B] ++;
    }

    for(int i = 1; i <= N; ++ i) if(Deg[i] % 2) return 0 * printf("-1");

    Euler();

    Order.pop_back();
    for(int i = 0; i < Order.size(); ++ i) printf("%i ", Order[i]);
}