#include <bits/stdc++.h>
#define st first
#define nd second
#define pb push_back
#define N 100001
#define M 500001
using namespace std;
typedef long long ll;
int n, m, i, j, x, y;
bool used[M];
pair<int,int> muchii[M];
vector<int> ans;
vector<int> v[N];
FILE *fin=fopen("ciclueuler.in","r");
FILE *fout=fopen("ciclueuler.out","w");
void dfs(int nod, int src)
{
    for(auto i:v[nod])
        if(!used[i])
    {
        blocaj=0;
        used[i]=1;
        if(muchii[i].st==nod)
            dfs(muchii[i].nd,i);
        else dfs(muchii[i].st,i);
    }
   // if(blocaj)
     //   {
            ans.pb(nod);
       // }
}
int main()
{
    fscanf(fin,"%d%d",&n,&m);
    for(i=1;i<=m;++i)
    {
        fscanf(fin,"%d%d",&x,&y);
        v[x].pb(i);
        v[y].pb(i);
        muchii[i]={x,y};
    }
    for(i=1;i<=n;++i)
        if(v[i].size()%2||v[i].empty())
    {
        fprintf(fout,"-1\n");
        return 0;
    }
    dfs(1,0);
    for(i=1;i<=m;++i)
        if(!used[i])
    {
        fprintf(fout,"-1\n");
        return 0;
    }
    for(i=0;i<ans.size();++i)
        fprintf(fout,"%d ",ans[i]);
    return 0;
}