#include <fstream>
#include <vector>
#include <stack>
#include <bitset>

using namespace std;

ifstream fin("ciclueuler.in");
ofstream fout("ciclueuler.out");

int N, M, x, y, k, A[100010];
bitset<500010>v;
vector< pair <int, int> >L[100010];
stack<int> Q;

void dfs(int node)
{
    v[node] = 1;

    for(int i = 0; i < L[node].size(); i ++)
    {
        if(v[ L[node][i].first ] == 0)
        {
            dfs(L[node][i].first);
        }
    }
}

int main()
{
    fin >> N >> M;

    for(int i = 1; i <= M; i ++)
    {
        int x, y;
        fin >> x >> y;
        L[x].push_back(make_pair(y, i));
        L[y].push_back(make_pair(x, i));
        A[x] ++;
        A[y] ++;
    }

    for(int i = 1; i <= N; i ++)
    {
        if(v[i] == 0)
        {
            dfs(i);
            k = i;
            break;
        }
    }

    for(int i = 1; i <= N; i ++)
    {
        if( (A[i] % 2) || (v[i] == 0 && A[i]) )
           {
               fout << -1;
               return 0;
           }
    }
    v.reset();

    Q.push(k);

    bool ok = true;

    while(!Q.empty())
    {
        k = Q.top();
        if(A[k] == 0)
        {
            if(ok == false)
            {
                fout << k << " ";

            }
            ok = false;
            Q.pop();
            continue;
        }

        while(v[ L[k][ L[k].size() - 1].second ] == 1)
        {
            L[k].pop_back();
        }

        v[ L[k][ L[k].size() - 1].second ] = 1;
        Q.push(L[k][ L[k].size() - 1].first);
        A[k] --;
        A[ L[k][ L[k].size() - 1 ].first ] --;
        L[k].pop_back();

    }

    return 0;
}