#include <iostream>
#include <cstdio>
#include <vector>
#include <bitset>

using namespace std;

int n,m,x,y;
vector <pair<int,int>> muchii;
vector <int> g[100005];
int d[100005];
vector <int> q;
bitset <500005> viz;

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

    scanf("%d%d", &n,&m);
    for(int i=0;i<m;++i){
        scanf("%d%d", &x,&y);
        muchii.push_back({x,y});
        g[x].push_back(i);
        g[y].push_back(i);
        d[x]++, d[y]++;
    }

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

    q.push_back(1);
    while(!q.empty()){
        x = q.back();
        if(g[x].empty()){
            q.pop_back();
            if(!q.empty())
            cout<<x<<" ";
        }
        else{
            y = g[x].back();
            g[x].pop_back();
            if(!viz[y]){
                viz[y]=1;
                if(muchii[y].first == x)
                    q.push_back(muchii[y].second);
                else
                    q.push_back(muchii[y].first);
            }
        }
    }

    return 0;
}