#include<cstdio>
#include<vector>
#include<queue>
using namespace std;
FILE*in=fopen("ciclueuler.in","r");
FILE*out=fopen("ciclueuler.out","w");
int n,m,x,y,i,grad[100005],ct;
bool use[500005],b[100005];
struct muchie
{
    int nr;
    int nrord;
};
muchie z;
vector<muchie> v[100005];
queue<int> q;
void bfs()
{
    while(!q.empty())
    {
        int g=q.front();
        q.pop();
        for(int t=0;t<v[g].size();t++)
        {
            if(b[v[g][t].nr]==0)
            {
                q.push(v[g][t].nr);
                b[v[g][t].nr]=1;
            }
        }
    }
}
void euler(int nod)
{
    while(grad[nod]>0)
    {
            if(use[v[nod].back().nrord]==0)
            {
                grad[nod]--;
                grad[v[nod].back().nr]--;
                use[v[nod].back().nrord]=1;
                euler(v[nod].back().nr);
            }
            v[nod].pop_back();
    }
    ct++;
    if(ct<=m)
    {
        fprintf(out,"%d ",nod);
    }
}
int main()
{
    fscanf(in,"%d%d",&n,&m);
    for(i=1;i<=m;i++)
    {
        fscanf(in,"%d%d",&x,&y);
        z.nr=y;
        z.nrord=i;
        v[x].push_back(z);
        grad[x]++;
        z.nr=x;
        v[y].push_back(z);
        grad[y]++;
    }
    for(i=1;i<=n;i++)
    {
        if(grad[i]%2==1)
        {
            fprintf(out,"-1");
            return 0;
        }
    }
    b[1]=1;
    q.push(1);
    bfs();
    for(i=1;i<=n;i++)
    {
        if(b[i]==0)
        {
            fprintf(out,"-1");
            return 0;
        }
    }
    euler(1);
}