#include <iostream>
#include <fstream>
#include <vector>

using namespace std;

const int NMAX = 1e5;
const int EMAX = 5e5;

vector <pair<int, int>> edges[NMAX + 1];
int viz[EMAX];
int deg[NMAX + 1];

vector <int> ciclu;

void euler( int node ) {
    while ( !edges[node].empty() ) {
        int nxt = edges[node].back().first;
        int edge = edges[node].back().second;
        edges[node].pop_back();
        if ( !viz[edge] ) {
            viz[edge] = 1;
            euler( nxt );
        }
    }
    ciclu.push_back( node );
}
int main() {
    int n, m, i, a, b;
    cin >> n >> m;
    for ( i = 0; i < m; i ++ ) {
        cin >> a >> b;
        edges[a].push_back( { b, i } );
        edges[b].push_back( { a, i } );
        deg[a] ++;
        deg[b] ++;
    }
    i = 1;
    while ( i <= n && deg[i] % 2 == 0 )
        i ++;
    if ( i <= n ) {
        cout << -1;
    } else {
        euler( 1 );
        for ( i = 0; i < m; i ++ ) {
            cout << ciclu[i] << ' ';
        }
    }
    return 0;
}