#include <iostream> // Algoritmul lui Hierholzer
#include <fstream>
#include <vector>
#include <stack>
#define nMax 100005
#define mMax 500005
using namespace std;
int n, m, x, y, node, new_node, to[mMax], from[mMax],edge;
vector <int> v[nMax], sol;
bool usedEdge[mMax];
stack <int> cycle;

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

    fin >> n >> m;
    for(int i = 1; i <= m; ++i){
        fin >> x >> y;
        v[x].push_back(i);
        v[y].push_back(i);
        from[i] = x;
        to[i] = y;
    }
    for(int i = 1; i <= n; ++i)
    if(v[i].size() % 2 != 0) {fout << -1; return 0;}

   cycle.push(1);
   while(!cycle.empty()){
    node = cycle.top();
    if(!v[node].empty()){
        edge = v[node].back();
        v[node].pop_back();
        if (!usedEdge[edge]) {
                usedEdge[edge] = true;
                if(to[edge] != node) new_node = to[edge];
                  else new_node = from[edge];
                cycle.push(new_node);
            }

        continue;
    }

    sol.push_back(node);
    cycle.pop();
   }

    for(int i = 0; i < sol.size() - 1; ++i)
    fout << sol[i] << ' ';
    return 0;
}