#include <cstdio>
#include <iostream>
#include <vector>
using namespace std;
pair <int, int> v[500001];
int cnt;
int e[1000001];
bool marcat[500001], viz[100001];
vector <int> a[100001];
const int dim = 1 << 17;
char getch() {
    static char buff[dim];
    static int bp = dim;
    if ( bp == dim ) {
        bp = 0;
        fread ( buff, 1, dim, stdin );
    }
    return buff[bp++];
}
void get ( int &a ) {
    //a=0;
    char ch;
    do {
        ch = getch();
    } while ( ch < '0' || ch > '9' );
    do {
        a = a * 10 + ch - '0';
        ch = getch();
    } while ( '0' <= ch && ch <= '9' );
}
void dfs ( int x ) {
    int muchie, y;
    viz[x] = 1;
    for ( int i = 0; i < a[x].size(); i++ ) {
        muchie = a[x][i];
        y = v[muchie].second;
        if ( x == y )
            y = v[muchie].first;
        if ( !viz[y] )
            dfs ( y );
    }
}
void euler ( int x ) {
    //cout<<x<<'\n';
    int muchie, y;
    for ( int i = 0; i < a[x].size(); i++ ) {
        muchie = a[x][i];
        if ( !marcat[muchie] ) {
            marcat[muchie] = 1;
            y = v[muchie].second;
            if ( x == y )
                y = v[muchie].first;
            euler ( y );
        }
    }
    e[++cnt] = x;
}
int n, m, i, x, y, cnt1 = 0;
int main() {
    freopen ( "ciclueuler.in", "r", stdin );
    freopen ( "ciclueuler.out", "w", stdout );
    get ( n );
    get ( m );
    for ( i = 1; i <= m; i++ ) {
        x = 0;
        y = 0;
        get ( x );
        get ( y );
        v[i].first = x;
        v[i].second = y;
        a[x].push_back ( i );
        a[y].push_back ( i );
    }
    dfs ( 1 );
    for ( i = 1; i <= n; i++ )
        if ( a[i].size() % 2 || !viz[i] ) {
            cout << "-1";
            return 0;
        }
    euler ( 1 );
    for ( i = 1; i <= cnt - 1; i++ )
        cout << e[i] << " ";
    return 0;
}