#include <fstream>
#include <vector>
#include <stack>
using namespace std;


struct abc
{
    int x;
    int y;
    bool f;
} v[500005];


ifstream fin("ciclueuler.in");
ofstream fout("ciclueuler.out");


int grad[100005],n,m;
int ciclu[500005],cnt=0;
vector<int>G[100005];
stack<int>stiva;


int main()
{
    fin>>n>>m;
    for(int i=1; i<=m; i++)
    {
        int x,y;
        fin>>x>>y;
        grad[x]++;
        grad[y]++;
        v[i].x=x;
        v[i].y=y;
        G[x].push_back(i);
        G[y].push_back(i);
    }
    for(int i=1; i<=n; i++)
        if(grad[i]%2==1)
        {
            fout<<-1;
            return 0;
        }
    stiva.push(1);
    while(!stiva.empty())
    {
        int nod = stiva.top();
        int ok=0;
        while(G[nod].size())
        {
            int muchie = G[nod].back();
            G[nod].pop_back();
            if(v[muchie].f == 0)
            {
                v[muchie].f=1;
                ok = 1;
                int x = v[muchie].x;
                int y=v[muchie].y;
                if(x!=nod) stiva.push(x);
                else stiva.push(y);
                break;
            }
        }
        if(ok==0)
            ciclu[++cnt]=nod,stiva.pop();

    }
    if(cnt!=m+1)
    {
        fout<<-1;
        return 0;
    }
    for(int i=1; i<cnt; i++) fout<<ciclu[i]<<" ";
    return 0;
}