#include <bits/stdc++.h>
using namespace std;
vector <int> G[100005];
stack <int> S;
vector <int> ::iterator it;
bool OK=true;
int n,m,i,x,y,node;
void euler(int node)
{
    int i,son;
    while (G[node].size())
    {
        S.push(node);
        son=G[node].back();
        G[node].pop_back();
        it=find(G[son].begin(),G[son].end(),node);
        G[son].erase(it);
        node=son;
    }
}
int main()
{
    freopen("ciclueuler.in","r",stdin);
    freopen("ciclueuler.out","w",stdout);
    scanf("%d %d",&n,&m);
    for (i=1; i<=m; i++)
    {
        scanf("%d %d",&x,&y);
        G[x].push_back(y);
        G[y].push_back(x);
    }
    for (i=1; i<=n; i++) if (G[i].size()%2==1)
    {
        printf("-1\n");
        return 0;
    }
    node=1;
    while (!S.empty() || OK)
    {
        OK=false;
        printf("%d ",node);
        euler(node);
        node=S.top();
        S.pop();
    }
    return 0;
}