#include <cstdio>
#include <algorithm>
#include <vector>
#include <bitset>
#include <stack>

#define Nmax 100005

using namespace std;
vector<int> G[Nmax];
bitset<Nmax> used;
stack<int> S;
int N,M;

void Read()
{
    scanf("%d%d",&N,&M);
    int a,b;
    for(int i = 1; i <= M; ++i){
        scanf("%d%d",&a,&b);
        G[a].push_back(b);
        G[b].push_back(a);
    }
}

void DFS(int k ){
    used[k] = 1;
    for(vector<int>::iterator it = G[k].begin(); it != G[k].end(); ++it)
        if(!used[*it])
            DFS(*it);
}

int Check()
{
    DFS(1);
    for(int i = 1; i <= N; ++i)
        if(G[i].size() % 2 == 1 || !used[i] )
            return 0;
    return 1;

}

void sterge(int k,int v){
    G[k].erase(G[k].begin());
    G[v].erase(find(G[v].begin(),G[v].end(),k));
}

void euler(int k)
{
    int v;
    do{
        while(G[k].size()){
            S.push(k);
            v = G[k][0];
            sterge(k,v);
            k = v;
        }
        k = S.top();
        S.pop();
        printf("%d ",k);
    }while(!S.empty());
}

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

    Read();
    if(Check())
        euler(1);
    else
        printf("-1\n");

    return 0;
}