#include <fstream>
#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(buff,SIZE,1,input_file);
        }

        inline InputReader &operator >>(int& n)
        {
            n = 0;
            while (buff[cursor] < '0' || buff[cursor] > '9')
                advance();
            while (buff[cursor] >= '0' && buff[cursor] <= '9') {
                n = n * 10 + buff[cursor] - '0';
                advance();
            }
            return *this;
        }

    private:
        static const int SIZE = 1<<17;
        int cursor;
        FILE *input_file;
        char buff[SIZE];

        inline void advance() {
            cursor++;
            if (cursor == SIZE) {
                cursor = 0;
                fread(buff,SIZE,1,input_file);
            }
        }
};

int n,m;
vector<int> G[100001];
int grad[100001];
stack<int> S;

void del(int node,int from)
{
    for (int i = 0; i < G[from].size(); i++)
        if (G[from][i] == node) {
            G[from].erase(G[from].begin() + i);
            return;
        }
}

vector<int> Sol;

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

    int x,y;
    fin >> n >> m;
    for (int i = 1; i <= m; i++)
    {
        fin >> x >> y;
        G[x].push_back(y);
        G[y].push_back(x);
        grad[x]++,grad[y]++;
    }

    for (int i = 1; i <= n; i++)
        if (grad[i] % 2 != 0)
        {
            fout << -1;
            return 0;
        }

    S.push(1);
    while (!S.empty())
    {
        int u = S.top();
        if (G[u].size())
        {
            del(u,G[u].back());
            S.push(G[u].back());
            G[u].pop_back();
            continue;
        }
        Sol.push_back(u);
        S.pop();
    }

    for (int i = 1; i <= m; i++)
        fout << Sol[i-1] << " ";

}