#include<cstdio>
#include<vector>
#include<stack>
using namespace std;
int N,M,x,y;
vector <int> G[100001];
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);
        G[x].push_back(y),G[y].push_back(x);
    }
    for(int i=1;i<=N;++i)
        if((G[i].size())&1){
            printf("-1");
            return 0;
        }
    stack <int> stiva;
    stiva.push(1),x=0;
    while(!stiva.empty()){
        int nod=stiva.top();
        if(G[nod].size()){
            y=G[nod][G[nod].size()-1];
            G[nod].erase(G[nod].begin()+G[nod].size()-1);
            bool ok=1;
            for(int i=0;i<G[y].size()&&ok;++i)
                if(G[y][i]==nod)
                    ok=0,G[y].erase(G[y].begin()+i);
            stiva.push(y);
        }else{
            stiva.pop();
            if(x<M)printf("%d ",nod);
            ++x;
        }
    }
    return 0;
}