#include <bits/stdc++.h>

#define int_pair std::pair <int, int>

#define MAXN 100005
#define MAXM 500005

int N, M;
std::vector <int> ADC[MAXN], Ans;
std::vector <int_pair> Edges;

inline void AddEdge(int X, int Y, int idx) {
    ADC[X].push_back(idx);
    ADC[Y].push_back(idx);
    Edges.push_back({X, Y});
}

bool Check() {
    for (int i=1; i<=N; ++i)
        if (ADC[i].size()&1)
            return false;
    return true;
}

std::stack <int> S;
bool Seen[MAXM];
void FindCycle() {
    S.push(1);
    int Top, idx;

    while (!S.empty()) {
        Top = S.top();

        if (ADC[Top].empty())
            S.pop(), Ans.push_back(Top);
        else {
            idx = ADC[Top].back();
            ADC[Top].pop_back();

            if (!Seen[idx])
                Seen[idx] = 1,
                S.push(Edges[idx].first + Edges[idx].second - Top);
        }
    }
}

std::ifstream In ("ciclueuler.in");
std::ofstream Out("ciclueuler.out");

void Citire() {
    In >> N >> M;
    for (int i=0, X, Y; i<M; ++i)
        In >> X >> Y, AddEdge(X, Y, i);
}

void Rezolvare() {
    if (Check()) {
        FindCycle();
        for (int i=0; i<Ans.size()-1; ++i)
            Out << Ans[i] << ' ';
    }
    else
        Out << "-1\n";
}

int main()
{
    Citire();
    Rezolvare();

    return 0;
}