#include <bits/stdc++.h>
#define pb push_back

using namespace std;

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

void debug_out() { cerr << '\n'; }
template <typename Head, typename... Tail> void debug_out(Head H, Tail... T) { cerr << " " << H; debug_out(T...);}
#define dbg(...) cerr << #__VA_ARGS__ << " ->", debug_out(__VA_ARGS__)
#define dbg_v(x, n) do{cerr<<#x"[]: ";for(int _=0;_<n;++_)cerr<<x[_]<<" ";cerr<<'\n';}while(0)
#define dbg_ok cerr<<"OK!\n"

typedef pair<int,int> pii;
typedef long long int ll;
typedef long double ld;

const int DMAX = 1e5+10;

vector <pii> arb[DMAX];
vector <int> ans;

int V[DMAX];
bool id[5*DMAX];

int n,m;

void euler(int node);

int main(){
    ios_base::sync_with_stdio(false);
    cin.tie(0);

    int t,i,j;
    int x,y;

    fin>>n>>m;
    for(i=1;i<=m;i++){
        fin>>x>>y;
        arb[x].pb({y,i});
        arb[y].pb({x,i});
    }
    for(i=1;i<=n;i++)
        if(arb[i].size() & 1){
            fout<<"-1\n";
            return 0;
        }
    euler(1);
    ans.pop_back();
    for(auto& it:ans)
        fout<<it<<' ';
    fout<<'\n';
    return 0;
}
void euler(int node){
    while(!arb[node].empty()){
        pii aux=arb[node].back();
        arb[node].pop_back();
        if(id[aux.second])
            continue;
        id[aux.second]=true;
        euler(aux.first);
    }
    ans.pb(node);
}