#include <stdio.h>
#define MAXN 100000
#define MAXM 500000
int ult[MAXN], deg[MAXN], nod[2 * MAXM], next[2 * MAXM], prev[2 * MAXM];
int st[MAXM + 1], d = 0;
int ac[MAXM + 1], k[MAXM + 1], da = 0;
char fol[MAXM];

void ceuler(int x){
  ac[da] = x;
  k[da] = ult[x];
  da++;
  int poz;
  while(da > 0){
    if(k[da - 1] == -1){
      st[d] = ac[da - 1] + 1;
      d++;
      da--;
    }
    else{
      x = ac[da - 1];
      poz = k[da - 1];
      k[da - 1] = next[k[da - 1]];
      if(fol[poz / 2]){
        if(prev[poz] == -1)
          ult[x] = next[poz];
        else
          next[prev[poz]] = next[poz];
      }
      else{
        fol[poz / 2] = 1;
        ac[da] = nod[poz];
        k[da] = ult[nod[poz]];
        da++;
      }
    }
  }
}

int main(){
  FILE *in = fopen("ciclueuler.in", "r");
  int n, m, i, x, y, dr = 0;
  fscanf(in, "%d%d", &n, &m);
  for(i = 0; i < n; i++)
    ult[i] = -1;
  for(i = 0; i < m; i++){
    fscanf(in, "%d%d", &x, &y);
    x--;  y--;
    deg[x]++;
    deg[y]++;
    nod[dr] = x;
    next[dr] = ult[y];
    prev[ult[y]] = dr;
    ult[y] = dr;
    prev[dr] = -1;
    dr++;
    nod[dr] = y;
    next[dr] = ult[x];
    prev[ult[x]] = dr;
    ult[x] = dr;
    prev[dr] = -1;
    dr++;
  }
  fclose(in);
  FILE *out = fopen("ciclueuler.out", "w");
  char g = 0;
  for(i = 0; i < n; i++){
    if(deg[i] & 1)
      g = 1;
  }
  if(!g){
    ceuler(0);
    for(i = 0; i < d - 1; i++)
      fprintf(out, "%d ", st[i]);
  }
  else
    fprintf(out, "-1");
  return 0;
}