#include <fstream>
#include <vector>
#include <stack>
#define NMAX 100005
#define MMAX 500005

using namespace std;

FILE* f=freopen("ciclueuler.in","r",stdin);
FILE* o=freopen("ciclueuler.out","w",stdout);

int n,m;
vector<int> graph[NMAX];
vector<int> sol;


void EulerianPath(int x)
{
    for(int i=0;i<graph[x].size();++i)
    {
        int ind=graph[x][i];
        if(ind!=-1)
        {
            graph[x][i]=-1;
            for(int j=0;j<graph[ind].size();++j)
            {
                if(graph[ind][j]==x) {
                    graph[ind][j]=-1;
                    break;
                }
            }
            EulerianPath(ind);
        }
    }
    sol.push_back(x);
}

int main()
{
    scanf("%d%d",&n,&m);

    for(int i=0;i<m;++i)
    {
        int x,y;
        scanf("%d%d",&x,&y);
        graph[x].push_back(y);
        graph[y].push_back(x);
    }
    for(int i=1;i<=n;++i) if(graph[i].size()%2||graph[i].size()==0) { printf("-1"); return 0; }

    EulerianPath(1);

    for(int i=0;i<sol.size()-1;++i)
    {
        printf("%d ",sol[i]);
    }

    return 0;
}