#include<cstdio>
#include<cassert>
#include<vector>
#include<queue>
#include<algorithm>

using namespace std;

int n, m;
vector<pair<int, int> > graph[100005];
pair<int, int> edg[500005];
int num[100005], ind[100005], viz[500005];

void read(){
  assert(freopen("ciclueuler.in", "r", stdin));

  scanf("%d%d", &n, &m);

  for(int i = 1; i <= m; ++i){
    int x, y;
    scanf("%d%d", &x, &y);
    ++num[x];
    ++num[y];
    edg[i] = make_pair(x, y);
    graph[x].push_back(make_pair(i, y));
    graph[y].push_back(make_pair(i, x));
  }

}

vector<int> ans;

int aux;

void dfs(int e, int x){
  while(ind[x] < graph[x].size()){
    if(!viz[graph[x][ind[x]].first]){
      viz[graph[x][ind[x]].first] = 1;
      aux = ind[x];
      ++ind[x];
      dfs(graph[x][aux].first, graph[x][aux].second);
    }
    else
      ++ind[x];
  }

  if(x == edg[e].first)
    ans.push_back(edg[e].second);
  else
    ans.push_back(edg[e].first);
}

void write(){
  assert(freopen("ciclueuler.out", "w", stdout));

  if(ans.size() - 1 != m){
    printf("-1\n");
    return;
  }

  for(int i = 0; i < ans.size() - 1; ++i)
    printf("%d ", ans[i]);
}

int main(){
  read();
  int isk = 1;
  for(int i = 1; i <= n; ++i)
    if(num[i] % 2 != 0)
      isk = 0;
  if(isk)
    dfs(0, 1);
  write();

  return 0;
}