#include<fstream>
#include<vector>
#include<algorithm>
#include<deque>
#define nx 500007
using namespace std;
int n,m,x,y,i,j,l,grad[nx],viz[nx];
vector<int>v[nx];
deque<int>d;

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

void dfs(int x)
{
    viz[x]=1;
    for(int j=0;j<v[x].size();j++)
        if(!viz[v[x][j]])
            dfs(v[x][j]);
}

int main()
{
    fin>>n>>m;
    for(i=1;i<=m;i++)
    {
        fin>>x>>y;
        v[x].push_back(y);
        v[y].push_back(x);
        grad[x]++;
        grad[y]++;
    }
    for(i=1;i<=n;i++)
    if(grad[i]%2)
    {
        fout<<'-1';
        return 0;
    }

    dfs(1);
    for(i=1;i<=n;i++)
    if(!viz[i] || grad[i]%2)
    {
        fout<<'-1';
        return 0;
    }

    d.push_back(1);
    while(d.size())
    {
        x=d.back();
        if(v[x].size())
        {
        y=v[x].back();
        v[x].pop_back();
        v[y].erase(find(v[y].begin(),v[y].end(),x));
        d.push_back(y);
        }
        else
        {
            fout<<x<<' ';d.pop_back();
        }
    }
     return 0;
}