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

using namespace std;

class parser{
    public:
        parser() {}
        parser(const char *file_name){
            input_file.open(file_name);
            cursor=0;
            input_file.read(buffer,SIZE);}
        inline parser &operator >>(int &n){
            while(buffer[cursor]<'0' or buffer[cursor]>'9') inc();
            n=0;
            while('0'<=buffer[cursor] and buffer[cursor]<='9')
                n=n*10+buffer[cursor]-'0',inc();
            return *this;}
    private:
        ifstream input_file;
        static const int SIZE=0x8000;
        char buffer[SIZE];
        int cursor=0;
        inline void inc(){
            if(++cursor==SIZE)
                cursor=0,input_file.read(buffer,SIZE);
        }
};


struct edge{
    int from,to;}edges[500010];

int n,m;
vector <int> v[500010],sol,stack;
vector <bool> elim(500010);

void euler(int nod)
{
    while(v[nod].size())
    {
        int a=v[nod].back();
        v[nod].pop_back();
        if(!elim[a])
        {
            int vec=edges[a].from^edges[a].to^nod;
            elim[a]=1;
            stack.push_back(nod);
            nod=vec;
        }
    }
}

int main()
{
    parser f ("ciclueuler.in");
    ofstream t ("ciclueuler.out");
    f>>n>>m;
    for (int i=0;i<m;++i)
        f>>edges[i].from>>edges[i].to,v[edges[i].from].push_back(i),v[edges[i].to].push_back(i);
    for (int i=0;i<n;++i)
        if (v[i].size()&1){
            t<<-1;return 0;}
    int x=1;
    while(1)
    {
        euler(x);
        if(stack.empty()) break;
        x=stack.back();
        stack.pop_back();
        sol.push_back(x);
    }
    for (auto i:sol)
        t<<i<<" ";
    return 0;
}