#include <fstream>
#include <vector>
#include <stack>

using namespace std;
ifstream in("ciclueuler.in");
ofstream out("ciclueuler.out");
const int N=100005;
vector<int>v[N],sol;
int n,m,vx[5*N],vy[5*N];
bool used[5*N];
stack<int>st;

int main()
{
    in>>n>>m;
    for(int i=1,x,y;i<=m;i++)
    {
        in>>x>>y;
        v[x].push_back(i);
        v[y].push_back(i);
        vx[i]=x;
        vy[i]=y;
    }
    for(int i=1;i<=n;i++)
        if(v[i].size()%2!=0)
        {
            out<<-1;
            return 0;
        }
    st.push(1);
    int vf,e,next;
    while(!st.empty())
    {
        vf=st.top();
        if(v[vf].size()==0)
        {
            st.pop();
            sol.push_back(vf);
            continue;
        }
        e=v[vf].back();
        v[vf].pop_back();
        if(!used[e])
        {
            used[e]=true;
            next=vx[e];
            if(vf==next)
                next=vy[e];
            st.push(next);
        }
    }
    for(unsigned i=0;i<sol.size();i++)
        out<<sol[i]<<' ';
    return 0;
}