#include<cstdio>
#include<algorithm>
#include<vector>

using namespace std;

const int maxN=100005;
const int maxM=500005;

pair<int,int> muchii[maxM];
vector<int> G[maxN];
vector<int> sol;

bool viz[maxM];
int P[maxN];

int n,m;

void read()
{
    int i,j,x,y;

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

    scanf("%d%d",&n,&m);

    for(i=1;i<=m;++i)
    {
        scanf("%d%d",&x,&y);
        muchii[i]=make_pair(x,y);
        G[x].push_back(i);
        G[y].push_back(i);
    }

}

bool verif()
{
    bool v=true; int i;

    for(i=1;i<=n;++i)
        if(P[i]%2!=0)
        {
            v=false;
            break;
        }

    return v;
}

inline void df(int nod)
{
    while(P[nod]<G[nod].size())
    {
        int mu=G[nod][P[nod]];
        if(viz[mu])
        {
            P[nod]++;
            continue;
        }
        viz[mu]=true;
        int vec=muchii[mu].first+muchii[mu].second-nod;
        P[nod]++;
        df(vec);
        sol.push_back(vec);
    }
}

int main()
{

    read();
    if(verif()==true)
    {
        df(1);
        if(sol.size()!=m)
        {
            printf("-1\n");
            return 0;
        }
        for(int i=0;i<sol.size();++i)
            printf("%d ",sol[i]);
    }
    else printf("-1\n");

    return 0;
}