#include <bits/stdc++.h>
using namespace std;
ifstream fin("ciclueuler.in");
ofstream fout("ciclueuler.out");
vector <int> v[100005];
int n,m,x,y,ct;
bool bct;
//int s[100005];
bool g[100005],viz[100005];
/*bool Grad()
{
    for(int i=1;i<=n;++i)
        if(g[i])return 1;
    return 0;
}*/
void DFS(int x)
{
    viz[x]=1;
    for(int i=0; i<v[x].size(); ++i)
        if(viz[v[x][i]]==0)
            DFS(v[x][i]);
}
void Euler(int x)
{
    if(!bct)
    {

        int y;
        while(v[x].size())
        {
            if(v[x].back()==-1)
                v[x].pop_back();
            else
            {
                y=v[x].back();
                v[x].pop_back();
                for(int i=0; i<v[y].size(); ++i)
                    if(v[y][i]==x)
                    {
                        v[y][i]=-1;
                        break;
                    }
                Euler(y);
            }

        }
        fout<<x<<" ";
        ct++;
        if(ct==m){
            fout.close();bct=1;}
    }
}
void Read()
{
    fin>>n>>m;
    for(int i=1; i<=m; ++i)
    {
        fin>>x>>y;
        if(g[x]==0)
            g[x]=1;
        else
            g[x]=0;
        if(g[y]==0)
            g[y]=1;
        else
            g[y]=0;
        if(x!=y)
        {
            v[x].push_back(y);

        }
        v[y].push_back(x);

    }
    for(int i=1; i<=n; ++i)
        if(g[i])
        {
            fout<<-1;
            return;
        }
    DFS(1);
    for(int i=1; i<=n; ++i)
        if(viz[i]!=1)
        {
            fout<<-1;
            return;
        }
    Euler(1);
}
int main()
{
    Read();
    return 0;
}