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

const int NMAX = 100010, MMAX = 500010;

int N, M, X, Y, EulerianCycle[MMAX];
vector<int> G[NMAX];
stack<int> St;

void Erase(int Node, int Dest)
{
    for(vector<int> :: iterator it = G[Node].begin(); it != G[Node].end(); ++ it)
        if(*it == Dest)
        {
            G[Node].erase(it);
            return ;
        }
}

void GetEulerTour(int Node)
{
    St.push(Node);
    while(!St.empty())
    {
        int Node = St.top();
        if(G[Node].size())
        {
            int Next = G[Node].back();
            G[Node].pop_back();
            Erase(Next, Node);
            St.push(Next);
        }else
        {
            EulerianCycle[++ EulerianCycle[0]] = Node;
            St.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(Y);
        G[Y].push_back(X);
    }

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

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