#include<fstream>
#include<vector>
#include<deque>
#include<cstring>
using namespace std;
vector<pair<int, int> > L[100005];
deque<int> q;
bool u[500005];
int n, m, x, y, i, D[100005], nod, vecin, muchie, prim;
void dfs(int nod)
{
    for(int i=0; i<L[nod].size(); i++)
    {
        int vecin=L[nod][i].first;
        if(u[vecin]==0)
        {
            u[vecin]=1;
            dfs(vecin);
        }
    }
}
ifstream in("ciclueuler.in");
ofstream out("ciclueuler.out");
int main()
{
    in>>n>>m;
    for(i=1; i<=m; i++)
    {
        in>>x>>y;
        L[x].push_back(make_pair(y, i));
        L[y].push_back(make_pair(x, i));
        D[x]++;
        D[y]++;
    }
    for(i=1; i<=n; i++)
    {
        if(D[i]>0)
        {
            u[i]=1;
            q.push_back(i);
            dfs(i);
            break;
        }
    }
    for(i=1; i<=n; i++)
    {
        if(D[i]%2==1)
        {
            out<<"-1";
            return 0;
        }
        if(D[i]>0 && u[i]==0)
        {
            out<<"-1";
            return 0;
        }
    }
    memset(u, 0, sizeof(u));
    prim=1;

    while(!q.empty())
    {
        nod=q.back();
        if(D[nod]==0)
        {
            if(prim==1)
                prim=0;
            else
            {
                out<<nod<<" ";
            }
            q.pop_back();
            continue;
        }
        while(u[L[nod].back().second]==1)
            L[nod].pop_back();
        vecin=L[nod].back().first;
        muchie=L[nod].back().second;
        q.push_back(vecin);
        u[muchie]=1;
        D[nod]--;
        D[vecin]--;
    }
    return 0;
}