#include <cstdio>
#include <vector>
#include <bitset>
#include <cctype>
#include <stack>

#define N 100005
#define M 500005

#define BUFF_SIZE 4096

using namespace std;

FILE *f = fopen("ciclueuler.in", "r");
FILE *g = fopen("ciclueuler.out", "w");

char buff[BUFF_SIZE];
int pos = BUFF_SIZE;

inline char getChar()
{
    if(pos == BUFF_SIZE)
    {
        fread(buff, 1, BUFF_SIZE, f);
        pos = 0;
    }
    return buff[pos++];
}
inline int READ_INT()
{
    int result = 0;
    char c;
    do{
        c = getChar();
    } while(!isdigit(c));
    do
    {
        result = result * 10 + (c - '0');
        c = getChar();
    } while(isdigit(c));
    return result;
}

struct muchie
{
    int st, dr;
} v[M];

int n;
vector <int> G[N];
bitset <M> viz;
stack <int> s;

bool e_pe_ciclu()
{
    for(int i = 1; i <= n; ++i)
        if(G[i].size() % 2 == 1) return 0;
    return 1;
}

int main()
{
    int m;
    n = READ_INT(); m = READ_INT();
    for(int i = 1; i <= m; ++i)
    {
        v[i].st = READ_INT(); v[i].dr = READ_INT();
        G[ v[i].st ].push_back(i);
        G[ v[i].dr ].push_back(i);
    }
    fclose(f);

    int nod, mch;
    if(e_pe_ciclu())
    {
        s.push(1);
        while(!s.empty())
        {
            nod = s.top();
            if(G[nod].empty())
            {
                if(s.size() > 1) fprintf(g, "%d ", nod);
                s.pop();
            }
            else
            {
                mch = G[nod].back();
                G[nod].pop_back();
                if(!viz[mch])
                {
                    viz[mch] = 1;
                    if(nod == v[mch].st) nod = v[mch].dr;
                    else nod = v[mch].st;
                    s.push(nod);
                }
            }
        }
    }
    else fprintf(g, "-1");
    fclose(g);
    return 0;
}