/*
    <b> Un graf este EULERIAN daca este CONEX si gradul fiecarul nod este PAR </b>
*/
#include <fstream>
#include <vector>
#include <bitset>
#include <queue>
#include <algorithm>
#include <ctime>
#include <utility>
#include <stack>

using namespace std;

ifstream cin("ciclueuler.in");
ofstream cout("ciclueuler.out");

const int MAXN = 100005;

int n, m;
vector <int> Graph[MAXN];
stack <int> Stack;

inline void ReadData()
{
    cin >> n >> m;
    for(int i = 1 ; i <= m ; ++ i)
    {
        int x, y;
        cin >> x >> y;
        Graph[x].push_back(y);
        Graph[y].push_back(x);
    }
}
inline bool CheckEulerProperty()
{
    for(int i = 1 ; i <= n ; ++ i)
        if(!Graph[i].size() || Graph[i].size() & 1)
            return false;
    return true;
}
inline void DepthFirstSearch()
{
    Stack.push(1);
    while( !Stack.empty() )
    {
        int x = Stack.top();
        if(Graph[x].size())
        {
            int y = Graph[x].back();
            Stack.push(y);
            Graph[x].pop_back();
            Graph[y].erase(find(Graph[y].begin(), Graph[y].end(), x));
        }
        else /// return from recursion
        {
            Stack.pop();
            if(!Stack.empty())
                cout << x << " ";
        }
    }
}
int main()
{
    ReadData();
    if( !CheckEulerProperty() )
    {
        cout << "-1\n";
        return 0;
    }
    DepthFirstSearch();
    return 0;
}