#include <cstdio>
#include <stack>
#include <vector>
#include<algorithm>
using namespace std;
FILE *f=fopen("ciclueuler.in","r");
FILE *g=fopen("ciclueuler.out","w");
#define maxn 100005
vector <int> G[maxn];
stack <int> S;
int x,y,n,m,ok=1;
void ciclu()
{
    S.push(1);
    while(S.empty()==0)
    {
        int nod=S.top();
        if(G[nod].size()!=0)
        {
            int y=G[nod][0];
            S.push(y);
            G[nod].erase(find(G[nod].begin(),G[nod].end(),y));
            G[y].erase(find(G[y].begin(),G[y].end(),nod));

        }
        else
        {
            fprintf(g,"%d ",S.top());
            S.pop();
        }
    }
}
int main()
{
    fscanf(f,"%d%d",&n,&m);
    for(int i=1;i<=m;i++){
        fscanf(f,"%d%d",&x,&y);
        G[x].push_back(y);
        G[y].push_back(x);
    }
    for(int i=1;i<=n && ok;i++)
        if(G[i].size()%2!=0)
            ok=0;
    if(ok)
    ciclu();
    else
        fprintf(g,"-1");
    return 0;
}