#include <bits/stdc++.h>
using namespace std;
typedef long long LL;
#define mp make_pair
#define CHECK(x) if(!(x)) return false;
#define CHECKRET(x, y) if(!(x)) return (y);
#define SKIP(x) if((x)) continue;
typedef pair<int, int> pii;

#ifdef INFOARENA
#define ProblemName "ciclueuler"
#endif

#define MCONCAT(A, B) A B
#ifdef ProblemName
#define InFile MCONCAT(ProblemName, ".in")
#define OuFile MCONCAT(ProblemName, ".out")
#else
#define InFile "fis.in"
#define OuFile "fis.out"
#endif

const int MAXBUF = 30000000;
char parseBuf[MAXBUF];
char *head;
bool isDigit[255];

void parseInit() {
  int a = fread(parseBuf, 1, MAXBUF, stdin);
  parseBuf[a] = 0;
  head = parseBuf;
  memset(isDigit, 0, sizeof isDigit);
  for (int i = '0'; i <= '9'; ++i)
    isDigit[i] = true;
}

int nextInt() {
  int ans = 0;
  for (; !isDigit[*head]; ++head);
  for (; isDigit[*head]; ++head)
    ans = ans * 10 + (*head) - '0';
  return ans;
}

const int MAXN = 100010;
const int MAXM = 500010;
bool impar[MAXN];
int nxt[MAXM * 2], G[MAXN];
int to[MAXM * 2];
int done[(MAXM * 2) >> 5];

void writeInt(int x) {
  char *ph = head;
  for (; x; x /= 10)
    *(ph++) = x % 10 + '0';
  reverse(head, ph);
  *(ph++) = ' ';
  head = ph;
}

void DFS(int x) {
  while (G[x] >= 0) {
    int iy = G[x]; G[x] = nxt[G[x]];
    SKIP(done[iy >> 5] & (1 << (iy & 31)));
    done[iy >> 5] |= (1 << (iy & 31));
    done[iy >> 5] |= (1 << ((iy ^ 1) & 31));
    DFS(to[iy]);
  }
  writeInt(x + 1);
}

int main() {
  assert(freopen(InFile, "r", stdin));
  assert(freopen(OuFile, "w", stdout));
  parseInit();
  memset(G, 0xFF, sizeof G);
  int N = nextInt(), M = nextInt();
  for (int i = 0; i < M; ++i) {
    int x = nextInt(), y = nextInt();
    --x, --y;
    impar[x] = !impar[x];
    impar[y] = !impar[y];
    to[2 * i] = y; nxt[2 * i] = G[x]; G[x] = 2 * i;
    to[2 * i + 1] = x; nxt[2 * i + 1] = G[y]; G[y] = 2 * i + 1;
  }
  for (int i = 0; i < N; ++i)
    if (G[i] == NULL || impar[i]) {
      puts("-1");
      return 0;
    }
  head = parseBuf;
  DFS(0);
  head -= 2;
  for (; *head != ' '; --head);
  fwrite(parseBuf, 1, head - parseBuf, stdout);
  return 0;
}