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


#define Nmax 100010
#define pb push_back
#define forit(it, v) for(typeof((v).begin()) it = (v).begin(); it != (v).end(); ++ it)

int N, M, X, Y, Ans[5 * Nmax];
vector<int> G[Nmax];
stack<int> S;

void Erase(int Node, int Son)
{
    forit(it, G[Node])
        if(*it == Son)
        {
            G[Node].erase(it);
            return ;
        }
}

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

int main()
{
    freopen("ciclueuler.in", "r", stdin);
    freopen("ciclueuler.out", "w", stdout);
    int i;
    scanf("%i %i", &N, &M);
    for(i = 1; i <= M; ++ i)
    {
        scanf("%i %i", &X, &Y);
        G[X].pb(Y);
        G[Y].pb(X);
    }
    for(i = 1; i <= N; ++ i)
        if(G[i].size() % 2)
        {
            printf("-1");
            exit(0);
        }
    Euler(1);
    for(i = 1; i <= Ans[0]; ++ i) printf("%i ", Ans[i]);
    return 0;
}