#include <fstream>
#include <vector>
#include <stack>
#define NMAX 100005
#define MMAX 500005

using namespace std;

FILE* f=freopen("ciclueuler.in","r",stdin);
FILE* o=freopen("ciclueuler.out","w",stdout);

int n,m;
vector<int> graph[NMAX];
vector<int> sol;
stack<int> stk;

void Erase(int x, int i)
{
    int ind=graph[x][i];
    graph[x][i]=-1;
    for(int j=0;j<graph[ind].size();++j)
    {
        if(graph[ind][j]==x) {
            graph[ind][j]=-1;
            break;
        }
    }
}

void EulerianPath(int x)
{
    int ok=1;
    while(ok) {
        ok=0;
        for(int i=0;i<graph[x].size();++i)
        {
            int ind=graph[x][i];
            if(ind!=-1)
            {
                ok=1;
                stk.push(x);
                Erase(x,i);
                x=ind;
                break;
            }
        }
    }
}

int main()
{
    scanf("%d%d",&n,&m);

    for(int i=0;i<m;++i)
    {
        int x,y;
        scanf("%d%d",&x,&y);
        graph[x].push_back(y);
        graph[y].push_back(x);
    }
    for(int i=1;i<=n;++i) if(graph[i].size()%2||graph[i].size()==0) { printf("-1"); return 0; }

    EulerianPath(1);
    while(!stk.empty())
    {
        int x=stk.top();
        sol.push_back(x);
        stk.pop();
        EulerianPath(x);
    }
    for(int i=0;i<sol.size()-1;++i)
    {
        printf("%d ",sol[i]);
    }

    return 0;
}