#include <stdio.h>
#include <stack>
#include <vector>
#include <algorithm>
#define nmax 100010

using namespace std;

int n,m,x,y;
int rang[nmax];
stack <int> st;
vector <int> g[nmax];

int main()
{
    freopen("ciclueuler.in","r",stdin);
    freopen("ciclueuler.out","w",stdout);

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

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

    for (int i=1;i<=n;i++)
        if (rang[i]%2==1) { puts("-1"); return 0; }

    st.push(1);

    while (!st.empty()) {
        int x=st.top();
        if (g[x].size()==0) {
            printf("%d ",x); st.pop(); continue;
        }

        int y=g[x][g[x].size()-1];
        st.push(y); g[x].pop_back();
        g[y].erase(find(g[y].begin(),g[y].end(),x));
    }

    return 0;
}