#include<stdio.h>
#include <list>
#include <stack>
#include <queue>
using namespace std;

list<int> L,G[100010];
stack<int> S;
int N, M, deg[100010], viz[100010], x, y;

void DFS(int v)
{
    viz[v]=1;

    for(list<int>::iterator it = G[v].begin(); it!=G[v].end();++it)
        if(viz[*it]==0)
            DFS(*it);
}

bool conex()
{

            return 0;
    return 1;
}

bool eulerian()
{
    DFS(1);

    for(int i=1;i<=N;++i)
        if(deg[i]%2==1 || viz[i]==0)
            return 0;

    return 1;
}

void sterg(int v, int w)
{
    --deg[v];
    --deg[w];
    G[v].pop_front();
    for(list<int>::iterator it = G[w].begin(); it!=G[w].end();++it)
        if(*it==v)
        {
            G[w].erase(it);
            break;
        }
}

void euler(int v)
{
    while(!G[v].empty())
    {
        int w = G[v].front();
        S.push(v);
        sterg(v,w);
        v=w;
    }
}

void solve()
{
    int v=1;
    do
    {
        euler(v);
        v=S.top();
        S.pop();
        L.push_back(v);

    } while(!S.empty());
}

int main()
{
    freopen("ciclueuler.in","r",stdin);
    freopen("ciclueuler.out","w",stdout);
    scanf("%d%d",&N,&M);
    for(int i=1;i<=M;++i)
    {
        scanf("%d%d",&x,&y);
        G[x].push_back(y);
        G[y].push_back(x);
        ++deg[x];
        ++deg[y];
    }

    if(!eulerian())
    {
        printf("%d",-1);
        return 0;
    }

    solve();

    for(list<int>::iterator it = L.begin(); it!=L.end();++it)
        printf("%d ",*it);
    return 0;
}