#include <fstream>
#include <vector>
#include <cstring>

#define DIMN 100010
#define DIMM 500010

using namespace std;

ifstream fin("ciclueuler.in");
ofstream fout("ciclueuler.out");

vector < pair<int,int> > L[DIMN];
vector < pair<int,int> >::iterator it;

int D[DIMN];
int viz[DIMM];
int s[2*DIMM];

int n, m, x, y, i, nod, number, ok, k;

void dfs(int nod) {
    viz[nod] = 1;

    for (vector < pair<int,int> >::iterator it = L[nod].begin(); it!= L[nod].end(); it++) {
        number++;
        if (viz[ it->first ] == 0) {
            dfs(it->first);
        }
    }
}

void euler(int nod) {

    pair<int,int> p;

    s[k = 1] = nod;
    while (k) {
        nod = s[k];
        while (  L[ nod ].size() ) {
            p = L[nod][ L[nod].size()-1 ];
            if (viz[p.second] == 1) {
                L[nod].pop_back();
                continue;
            } else {
                break;
            }
        }

        if (L[nod].size()) {
            s[++k] = p.first;
            viz[ p.second ] = 1;
        } else {
            fout<<s[k]<<" ";
            k--;
        }

    }

}

/*
void euler(int nod) {
    for (vector < pair<int,int> >::iterator it = L[nod].begin(); it!= L[nod].end(); it++) {
        if (viz[ it->second ] == 0) {
            viz[it->second] = 1;
            euler(it->first);
        }
    }
    fout<<nod<<" ";
}
*/

int main() {


    fin>>n>>m;
    for (i=1;i<=m;i++) {
        fin>>x>>y;
        D[x]++;
        D[y]++;
        L[x].push_back(  make_pair(y,i)  );
        L[y].push_back(  make_pair(x,i)  );
    }

    for (nod=1;nod<=n;nod++)
        if (D[nod] != 0)
            break;

    dfs(nod);



    if (number != 2*m) {
        fout<<"-1\n";
        return 0;
    }

    ok = 1;
    for (i=1;i<=n;i++)
        if (D[i] % 2 == 1) {
            fout<<"-1\n";
            return 0;
        }

    memset(viz, 0, sizeof(viz));
    euler(nod);

    return 0;
}