#include <fstream>
#include <iostream>
#include <vector>
#include <bitset>

std::ifstream fin ("grafeulerian.in");
std::ofstream fout ("grafeulerian.out");

const int MaxN = 100001;


int n;
std::vector<std::pair<int, int>> v[MaxN];
std::bitset<10 * MaxN> seen;
std::vector<int> sol;

void ReadData();
bool EsteEulerian();
void Euler(int x);
void Solve();
void Write();

int main ()
{
    ReadData();
    if (!EsteEulerian()) fout << "-1";
    else
    {
        Solve();
        Write();
    }

    fin.close();
    fout.close();

    return 0;
}

void ReadData()
{
    int m;
    fin >> n >> m;

    int x, y, i = 1;

    while (fin >> x >> y)
    {
        v[x].push_back({y, i});
        v[y].push_back({x, i});
        ++i;
    }
}

bool EsteEulerian()
{
    for(int x = 1; x <= n; ++x)
        if(v[x].size() % 2 == 1) return false;
    return true;
}

void Euler(int x)
{
    while(v[x].size() != 0)
    {
        int y = v[x].back().first;
        int c = v[x].back().second;
        v[x].pop_back();
        if (seen[c] == 1) continue;
        seen[c] = 1;
        Euler(y);
    }
    sol.push_back(x);
}

void Solve()
{
    Euler(1);
}

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