#include <cstdio>
#include <vector>

using namespace std;

struct punct
{
    int x,y;
};

punct edge[500010];
int vaz[100010],vaz1[100010],sol[100010],n,nr;
vector<int> v[500010];
vector<int> q;

void euler(int nod)
{
    while(v[nod].size()>0)
        if(vaz[v[nod].back()]) v[nod].pop_back();
        else
        {
            int vec;
            if(edge[v[nod].back()].x==nod) vec=edge[v[nod].back()].y;
            else vec=edge[v[nod].back()].x;
            vaz[v[nod].back()]=1;
            v[nod].pop_back();
            q.push_back(vec);
            euler(vec);
        }
}

void dfs(int nod)
{
    vaz1[nod]=1;
    for(int i=0;i<v[nod].size();i++)
    {
        int vec;
        if(edge[v[nod][i]].x==nod) vec=edge[v[nod][i]].y;
        else vec=edge[v[nod][i]].x;
        if(vaz1[vec]==0) dfs(vec);
    }
}

int solve()
{
    dfs(1);
    for(int i=1;i<=n;i++)
        if(v[i].size()%2==1 or vaz1[i]==0) return 0;
    while(q.size()>0)
    {
        int nod=q.back();
        q.pop_back();
        sol[++nr]=nod;
        euler(nod);
    }
    return 1;
}

int main()
{
    freopen("ciclueuler.in","r",stdin);
    freopen("ciclueuler.out","w",stdout);
    int m;
    scanf("%d%d",&n,&m);
    for(int i=1;i<=m;i++)
    {
        scanf("%d%d",&edge[i].x,&edge[i].y);
        v[edge[i].x].push_back(i);
        v[edge[i].y].push_back(i);
    }
    q.push_back(1);
    if(solve()==0) printf("-1");
    else for(int i=2;i<=nr;i++) printf("%d ",sol[i]);
    return 0;
}