#include <cstdio>
#include <vector>
#include <queue>

using namespace std;

struct egde
{
    int x,y;
}muc[500010];
vector<int> v[100010],q,sol;
char vaz[100010],elim[500010];

void bfs(int nod)
{
    queue<int> q;
    q.push(nod);
    vaz[nod]=1;
    while(!q.empty())
    {
        int nod=q.front();
        q.pop();
        for(vector<int>::iterator it=v[nod].begin();it!=v[nod].end();it++)
        {
            int vec=muc[*it].x^muc[*it].y^nod;
            if(!vaz[vec])
            {
                vaz[vec]=1;
                q.push(vec);
            }
        }
    }
}

void euler(int nod)
{
    while(v[nod].size())
    {
        int a=v[nod].back();
        v[nod].pop_back();
        if(!elim[a])
        {
            int vec=muc[a].x^muc[a].y^nod;
            elim[a]=1;
            q.push_back(nod);
            nod=vec;
        }
    }
}

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);
        v[muc[i].x].push_back(i);
        v[muc[i].y].push_back(i);
    }
    bfs(1);
    for(int i=1;i<=n;i++)
        if(!vaz[i] || v[i].size()%2)
        {
            printf("-1");
            return 0;
        }
    int x=1;
    while(1)
    {
        euler(x);
        if(q.empty()) break;
        x=q.back();
        q.pop_back();
        sol.push_back(x);
    }
    for(int i=0;i<sol.size();i++) printf("%d ",sol[i]);
    return 0;
}