#include <fstream>
#include <algorithm>
#include <vector>
#include <stack>

using namespace std;

class InputReader {
public:
    InputReader() {}
    InputReader(const char *file_name) {
        input_file = fopen(file_name, "r");
        cursor = 0;
        fread(buffer, SIZE, 1, input_file);
    }
    inline InputReader &operator >>(int &n) {
        while(buffer[cursor] < '0' || buffer[cursor] > '9') {
            advance();
        }
        n = 0;
        while('0' <= buffer[cursor] && buffer[cursor] <= '9') {
            n = n * 10 + buffer[cursor] - '0';
            advance();
        }
        return *this;
    }
private:
    FILE *input_file;
    static const int SIZE = 1 << 17;
    int cursor;
    char buffer[SIZE];
    inline void advance() {
        ++ cursor;
        if(cursor == SIZE) {
            cursor = 0;
            fread(buffer, SIZE, 1, input_file);
        }
    }
};

const int NMAX = 100000 + 5;
const int MMAX = 5 * NMAX;

struct Edge {
    int a, b;
    bool vis;

    int other(int node) {
        if (node == a)
            return b;
        else
            return a;
    }
} edges[MMAX];

int N, M;
vector <int> graph[NMAX];
int ii[NMAX];

stack <int> stk;
vector <int> sol;

int main()
{
    InputReader cin("ciclueuler.in");
    ofstream cout("ciclueuler.out");

    cin >> N >> M;
    for (int i = 1; i <= M; ++ i) {
        cin >> edges[i].a >> edges[i].b;

        graph[edges[i].a].push_back(i);
        graph[edges[i].b].push_back(i);
    }

    bool bad = false;
    for (int i = 1; i <= N; ++ i)
        if (graph[i].size() % 2 == 1) {
            bad = true;
            break;
        }

    if (bad) {
        cout << "-1\n";
        return 0;
    }

    stk.push(1);
    while (!stk.empty()) {
        int node = stk.top();

        bool found = false;
        for (; ii[node] < graph[node].size(); ++ ii[node])
            if (!edges[graph[node][ii[node]]].vis) {
                edges[graph[node][ii[node]]].vis = true;
                stk.push(edges[graph[node][ii[node]]].other(node));
                found = true;
                break;
            }

        if (!found) {
            stk.pop();
            sol.push_back(node);
        }
    }

    reverse(sol.begin(), sol.end());
    sol.pop_back();
    for (int i = 0; i < sol.size(); ++ i)
        cout << sol[i] << " \n"[i + 1 == sol.size()];
    return 0;
}