#include <fstream>
#include <cstring>
#include <vector>
#include <queue>

#define X1 100001

using namespace std;

ifstream in;
ofstream out;

vector <int> v[X1];
queue <int> q;
int grad[X1];

inline void euler(int nod)
{
    int x;

    for(;v[nod].size();)
    {
        x=*v[nod].begin();
        v[nod].erase(v[nod].begin());
        for(vector <int>::iterator it=v[x].begin();it!=v[x].end();++it)
            if(*it==nod)
            {
                v[x].erase(it);
                break;
            }
        euler(x);
    }

    q.push(nod);
}

int main()
{
    int M,N,x,y;

    memset(grad,0,sizeof(grad));

    in.open("ciclueuler.in");
    in>>N>>M;
    for(;M;--M)
    {
        in>>x>>y;
        v[x].push_back(y);
        v[y].push_back(x);
        ++grad[x];
        ++grad[y];
    }
    in.close();

    for(int i=1;i<=N;i++)
        if(grad[i]%2)
        {
            out.open("ciclueuler.out");
            out<<"-1\n";
            out.close();
            return 0;
        }

    euler(1);
    q.pop();

    out.open("ciclueuler.out");
    while(!q.empty())
    {
        out<<q.front()<<' ';
        q.pop();
    }
    out<<'\n';
    out.close();

    return 0;
}