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

#define Nmax 100005
#define DIM 1000005

using namespace std;
vector<int> G[Nmax],sol;
bitset<Nmax> used;
int stiva[6*Nmax];
int N,M,grad[Nmax];
char buff[DIM];
int pz = DIM - 1;

int scan(int &A)
{
    A = 0;
    while('0' > buff[pz] || buff[pz] > '9')
        if(++pz == DIM) fread(buff,1,DIM,stdin),pz = 0;
    while('0' <= buff[pz] && buff[pz] <= '9')
    {
        A = A * 10 + buff[pz] - 48;
        if(++pz == DIM) fread(buff,1,DIM,stdin),pz = 0;
    }
}


void read()
{
    scan(N);scan(M);
    int a,b;
    for(int i = 1; i <= M; ++i)
    {
        scan(a);scan(b);
        G[a].push_back(b);
        G[b].push_back(a);
        grad[a]++;
        grad[b]++;
    }
}
void sterge(int x,int y)
{
    for(int i = 0; i < G[x].size(); ++i)
        if(G[x][i] == y)
        {
            swap(G[x][i],G[x][G[x].size()-1]);
            G[x].pop_back();
            return;
        }
}



int vf;

void euler(int k)
{
    int nou;
    do
    {
        while(G[k].size())
        {
            stiva[++vf] = k;
            nou = G[k].back();
            G[k].pop_back();
            sterge(nou,k);
            k = nou;
        }
        k = stiva[vf--];
        printf("%d ",k);
    }while(vf);
}

void solve()
{
    for(int i = 1; i <= N; ++i)
        if(grad[i] % 2 == 1)
        {
            printf("-1\n");
            return;
        }
    /// deci se poate scoate ciclu'
    euler(1);
}

int main()
{
    freopen("ciclueuler.in","r",stdin);
    freopen("ciclueuler.out","w",stdout);

    read();
    solve();

    return 0;
}