#include <fstream>
#include <vector>
#include <bitset>
#include <stack>

#define f first
#define s second

using namespace std;

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

int n, m, x, y, grd[100005], L, l[100005], z;
vector<pair<int, int> > a[100005];
bitset<500005> v;
stack<int> st;

int main()
{
    F >> n >> m;
    for( int i = 1; i <= m; ++ i )
    {
        F >> x >> y;
        a[x].push_back({y, i});
        a[y].push_back({x, i});
        grd[x]++; grd[y]++;
    }
    for( int i = 1; i <= n; ++ i )
        if( grd[i] % 2 || !grd[i] )
        {
            G << -1;
            return 0;
        }
    st.push(1);
    while(!st.empty())
    {
        x = st.top();
        L = a[x].size();
        while(l[x] < L)
        {
            y = a[x][l[x]].f; z = a[x][l[x]].s;
            if(!v[z])
            {
                v[z] = 1;
                st.push(y);
                break;
            }
            l[x]++;
        }
        if(l[x] == L)
        {
            G << x << " ";
            st.pop();
        }
    }
    return 0;
}