#include <bits/stdc++.h>
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);
            }
        }
}f("ciclueuler.in");
ofstream g("ciclueuler.out");
int N,M,i,x,y,dim,X[1<<19],Y[1<<19];
bool viz[1<<19];
vector<int> S,Sol,G[1<<17];
inline void euler(int nod)
{
    S.push_back(nod);
    while(!S.empty())
    {
        nod=S.back();
        if(!G[nod].empty())
        {
            int w=G[nod].back();
            G[nod].pop_back();
            if(!viz[w])
            {
                viz[w]=1;
                S.push_back(X[w]+Y[w]-nod);
            }
        }
        else
        {
            Sol.push_back(nod);
            S.pop_back();
        }
    }
}
int main()
{
    f>>N>>M;
    for(i=1;i<=M;++i)
    {
        f>>X[i]>>Y[i];
        G[X[i]].push_back(i);
        G[Y[i]].push_back(i);
    }
    for(i=1;i<=N;++i)
        if(G[i].size()&1)
        {
            g<<-1;
            return 0;
        }
    euler(1);
    for(i=0;i<Sol.size()-1;++i) g<<Sol[i]<<' ';
    return 0;
}