#include <bits/stdc++.h>

using namespace std;

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

const int nMax = 100005;
int n, m, top;
int st[5 * nMax], dr[5 * nMax], grad[nMax];
int sol[5 * nMax];
vector <int> L[nMax];
vector <int> :: iterator it[nMax];
bool viz[nMax], used[5 * nMax];

inline void Read()
{
    int i, x, y;
    fin >> n >> m;
    for(i = 1; i <= m; i++)
    {
        fin >> st[i] >> dr[i];
        x = st[i];
        y = dr[i];
        L[x].push_back(i);
        L[y].push_back(i);
        ++grad[x];
        ++grad[y];
    }
}

inline void DfsC(int nod)
{
    int x;
    viz[nod] = true;
    for(auto i : L[nod])
    {
        x = st[i] + dr[i] - nod;
        if(viz[x]) continue;
        DfsC(x);
    }
}

inline bool Conex()
{
    int i;
    DfsC(1);
    for(i = 1; i <= n; i++)
        if(!viz[i]) return false;
    return true;
}

inline void Dfs(int nod)
{
    int x;
    while(it[nod] != L[nod].end())
    {
        if(used[*it[nod]])
        {
            ++it[nod];
            continue;
        }
        x = st[*it[nod]] + dr[*it[nod]] - nod;
        used[*it[nod]]=1;
        ++it[nod];
        Dfs(x);
    }
    sol[++top] = nod;
}

int main()
{
    Read();
    int i;
    for(i = 1; i <= n; i++)
        if(grad[i] % 2)
        {
            fout << "-1\n";
            return 0;
        }
    if(!Conex())
    {
        fout << "-1\n";
        return 0;
    }
    for(i = 1;i <= n; ++i)
        it[i] = L[i].begin();
    Dfs(1);
    for(i = 1; i < top; ++i)
        fout << sol[i] << " ";
    fout << "\n";
    return 0;
}