#include <cstdio>
#include <queue>
#include <algorithm>

using namespace std;

const int MaxN = 100005;

int N,M,X,Y,fr[MaxN],st[5*MaxN],top=0;
deque < pair <int,int> > v[MaxN];
bool found[5*MaxN];

void Euler(int nod)
{
    st[++top]=nod;
    while(top)
    {
        nod=st[top];
        while(!v[nod].empty()&&found[v[nod][0].second])
            v[nod].pop_front();
        if(!v[nod].empty())
        {
            st[++top]=v[nod][0].first;
            found[v[nod][0].second]=true;
            v[nod].pop_front();
        }
        else
        {
            if(top>1) printf("%d ",nod);
            top--;
        }
    }
}

int main()
{
    freopen("ciclueuler.in","r",stdin);
    freopen("ciclueuler.out","w",stdout);

    scanf("%d%d",&N,&M);
    for(int i=1;i<=M;i++)
    {
        scanf("%d%d",&X,&Y);
        v[X].push_back(make_pair(Y,i));
        v[Y].push_back(make_pair(X,i));
        fr[X]++,fr[Y]++;
    }
    bool pos=true;
    for(int i=1;i<=N;i++)
        if(fr[i]%2==1)
        {
            pos=false;
            break;
        }
    if(pos)
        Euler(1);
    else
        printf("-1");
    return 0;
}