#include <stdio.h>
#include <vector>
#include <stack>
#include <list>
#include <queue>
#include <cstring>
using namespace std;

#define Nmax 100001

vector < list<int> > graf;
list <int>::iterator it, last;
queue <int> coada;

int deg[Nmax], vizitat[Nmax];
int n, m;

void citire(){
    int x, y, j;
    char cc[100];
    scanf("%i %i", &n, &m);
    graf.resize(n+1);
    fgets(cc, 100, stdin);

    for(register int i = 1; i <= m; ++i){
        fgets(cc, 100, stdin);
        x = y = j = 0;
        while(cc[j] != ' ') x = x * 10 + cc[j] - '0', ++j;
        ++j;
        while(cc[j] != '\n') y = y * 10 + cc[j] - '0', ++j;

        ++deg[x]; ++deg[y];
        graf[x].push_back(y);
        graf[y].push_back(x);
    }
    fclose(stdin);
}

void bfs(int v){
    int first = v;
    coada.push(1);

    while(!coada.empty()){
        first = coada.front();
        coada.pop();
        it = graf[first].begin();
        last = graf[first].end();

        for(; it != last; ++it)
            if(!vizitat[*it]) coada.push(*it), vizitat[*it] = 1;
    }
}

int conex(){
    bfs(1);
    for(int i = 1; i <= n; ++i)
        if(!vizitat[i]) return 0;
    return 1;
}

int eulerian(){
    if( !conex() ) return 0;
    for(int i = 1; i <= n; ++i)
        if(deg[i] % 2 != 0) return 0;
    return 1;
}

void sterge(list<int>&l , int v){
    for(list<int>::iterator it2 = l.begin(); it2 != l.end(); ++it2)
        if(*it2 == v)
            l.erase(it2);
}

void euler(int v){
    int v1;

    while(!graf[v].empty()){
        v1 = *graf[v].begin();
        graf[v].pop_front();
        sterge(graf[v1], v);
        euler(v1);
    }

    printf("%i ", v);
}

void rez(){
    int v = eulerian();
    if(v == 0) printf("-1\n");
    else euler(1);
    return;
}

int main(){
    freopen("ciclueuler.in", "r", stdin);
    freopen("ciclueuler.out", "w", stdout);

    citire();
    rez();
}