#include <stdio.h>
#include <vector>
#include <algorithm>
#define max 100010
using namespace std;
vector<pair<int,int> > g[max];
vector<int>::iterator it;
int n,m,i,j,k,top,stack[5*max],deg[max];
char s[5*max];
void dfs(int v)
{
    int w,i;
    stack[++top]=v;
    while(top)
    {
        w=stack[top];
        if(!g[w].empty())
         if(!s[g[w].back().second])
         {
             s[g[w].back().second]=1;
             stack[++top]=g[w].back().first;
             g[w].pop_back();
         }
         else g[w].pop_back();
        else printf("%d ",stack[top--]);
    }
}
int main()
{
    freopen("ciclueuler.in","r",stdin);
    freopen("ciclueuler.out","w",stdout);
    scanf("%d%d",&n,&m);
    for(k=1; k<=m; k++)
    {
        scanf("%d%d",&i,&j);
        g[i].push_back(make_pair(j,k));
        g[j].push_back(make_pair(i,k));
        deg[i]++; deg[j]++;
    }
    for(i=1; i<=n; i++)
     if(deg[i]%2==1) { printf("-1"); return 0;}
    dfs(1);
    return 0;
}