#include <bits/stdc++.h>
#define cin fin
#define cout fout
using namespace std;
ifstream cin ("ciclueuler.in");
ofstream cout ("ciclueuler.out");
struct muchiee
{
    int x,y;
    int uz;
};
muchiee muc[500004];
stack<int>stackk;
vector<int>sol,G[500004];
int a,b,n,m,k,muchie,i;
void euler(int nodstart)
{
    stackk.push(nodstart);
    while(!stackk.empty())
    {
        k=stackk.top();
        int mar=G[k].size();
        if(G[k].size()==0)
        {
            sol.push_back(k);
            stackk.pop();
        }
        else
        {
            muchie=G[k].back();
            G[k].pop_back();
            if(muc[muchie].uz==0)
            {
                muc[muchie].uz=1;
                if(k==muc[muchie].x)
                    stackk.push(muc[muchie].y);
                    else
                    stackk.push(muc[muchie].x);
            }
        }
    }

}
int main()
{
    cin>>n>>m;
    for(i=1;i<=m;i++)
    {
        cin>>a>>b;
        G[a].push_back(i);
        G[b].push_back(i);
        muc[i].x=a;
        muc[i].y=b;
    }
    for(i=1;i<=n;i++)
        if(G[i].size()%2==1)
            break;
    if(i<=n)
    {
        cout<<"-1";
        exit(0);
    }
    euler(1);
    int mar=sol.size();
    for(i=mar-1;i>=1;i--)
        cout<<sol[i]<<" ";

    return 0;
}