#include <fstream>
#include <vector>
#include <queue>
#include <string.h>
#include <iostream>
#include <algorithm>

using namespace std;

ifstream in("ciclueuler
            .in");
ofstream out("ciclueuler.out");

const size_t MAXN = 101, MAXM = 501, INF = 1e9;
int deg[MAXN];
queue<int> ans;
vector<int> g[MAXN];
int n, m, nh = 1;

void euler(int v);
int main()
{
    in >> n >> m;
    for(int i = 1; i <= m; ++i)
    {
        int x, y;
        in >> x >> y;
        g[x].push_back(y);
        if(x != y)
            g[y].push_back(x);
        deg[x]+=2;
        if(x != y)
            deg[y]+=2;
    }

    // check eulerian
    for(int i = 1; i <= n; ++i)
    {
        if(deg[i] % 2)
        {
            out << -1;
            return 0;
        }
    }

    euler(1);
    int mh = m;
    while(mh > 0)
    {
        out << ans.front() << ' ';
        ans.pop();
        mh--;
    }
    return 0;
}

void
euler(int v)
{
    while(!g[v].empty())
    {
        int u = g[v].back();
        g[v].pop_back();
        if(u < 0) continue;
        for(int j = 0; j < g[u].size(); ++j)
            if(g[u][j] == v)
            {
                g[u][j] = -1;
                break;
            }
        euler(u);
    }
    ans.push(v);
}