#include <cstdio>
#include <vector>
#include <bitset>

using namespace std;

struct edge
{
    int x,y;
}muc[500010];
vector<int> g[100010],q;
bitset<500010> elim;
bitset<100010> vaz;

void dfs(int nod)
{
    vaz[nod]=1;
    for(vector<int>::iterator it=g[nod].begin();it!=g[nod].end();it++)
    {
        int vec=nod^muc[*it].x^muc[*it].y;
        if(!vaz[vec]) dfs(vec);
    }
}

void euler(int nod)
{
    while(g[nod].size())
    {
        int poz=g[nod].back();
        g[nod].pop_back();
        if(elim[poz]) continue;
        elim[poz]=1;
        q.push_back(nod);
        nod=nod^muc[poz].x^muc[poz].y;
    }
}

int main()
{
    freopen("ciclueuler.in", "r", stdin);
    freopen("ciclueuler.out", "w", stdout);
    int n,m;
    scanf("%d%d",&n,&m);
    for(int i=1;i<=m;i++)
    {
        scanf("%d%d",&muc[i].x,&muc[i].y);
        g[muc[i].x].push_back(i);
        g[muc[i].y].push_back(i);
    }
    dfs(1);
    for(int i=1;i<=n;i++)
        if(!vaz[i] || g[i].size()%2)
        {
            printf("-1");
            return 0;
        }
    int x=1;
    while(1)
    {
        euler(x);
        if(q.size()==0) break;
        x=q.back();
        q.pop_back();
        printf("%d ",x);
    }
    return 0;
}