#include<fstream>
#include<vector>
#include<list>
#include<stack>

using namespace std;
typedef int var;

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

struct Edge {
    var n, i;
    Edge(var a, var b) : n(a), i(b) {}
};

const var MAXN = 100001;

vector<bool> TAKEN;
vector<Edge> G[MAXN];
var n, m, D[MAXN];

void euler(const var &node) {

    for(vector<Edge>::iterator it = G[node].begin(); it != G[node].end(); ++it) {
        Edge &e = *it;
        if(!TAKEN[e.i]) {
            TAKEN[e.i] = 1;
            euler(e.n);
            fout<<e.n<<" ";
        }
    }
}

var count;
vector<bool> VIZ;
void dfs(var node) {
    VIZ[node] = 1;
    count ++;
    for(vector<Edge>::iterator it = G[node].begin(); it != G[node].end(); ++it) {
        if(!VIZ[(*it).n]) {
            dfs((*it).n);
        }
    }
}

int main() {
    var a, b;
    fin>>n>>m;
    TAKEN.resize(m+1, 0);
    VIZ.resize(n+1, 0);
    for(var i=1; i<=m; i++) {
        fin>>a>>b;
        G[a].push_back(Edge(b, i));
        G[b].push_back(Edge(a, i));
        D[a]++;
        D[b]++;
    }

    for(var i=1; i<=n; i++) {
        if(D[i] % 2) {
            fout<<-1;
            return 0;
        }
    }
    dfs(1);
    if(count < n) {
        fout<<-1;
        return 0;
    }

    euler(1);
    return 0;
}