#include <cstdio>
#include <vector>
#include <stack>
#include <algorithm>
using namespace std;
stack <int> S;
vector <int> G[100005];
int i,n,m,x,y,node;
bool OK;
void euler(int node)
{
    int i,son;
    while (G[node].size())
    {
        S.push(node);
        son=G[node].back();
        G[node].pop_back();
        G[son].erase(find(G[son].begin(),G[son].end(),node));
        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);

    }
    node=1;
    OK=true;
    for(i=1; i<=n; ++i)
        if(G[i].size()%2==1)
        {
            printf("-1\n");
            return 0;
        }
    while (!S.empty() || OK)
    {
        OK=false;
        printf("%d ",node);
        euler(node);
        node=S.top();
        S.pop();
    }
    return 0;
}