#include <cstdio>
#include <vector>

using namespace std;

int nr,euler[500010],n;
char vaz[500010],vaz1[100010];
vector<pair<int,int>> v[100010];
vector<int> q;

void dfs(int nod)
{
    vaz1[nod]=1;
    for(int i=0;i<v[nod].size();i++)
        if(vaz1[v[nod][i].first]==0) dfs(v[nod][i].first);
}

void lant_euler(int nod)
{
    while(v[nod].size()>0)
    {
        int vec=v[nod].back().first,poz=v[nod].back().second;
        v[nod].pop_back();
        if(vaz[poz]==0)
        {
            vaz[poz]=1;
            q.push_back(nod);
            nod=vec;
        }
    }
}

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

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