#include <fstream>
#include <vector>
#include <stack>
#include <algorithm>
#include <cstdio>
#include <cctype>
#include <cstring>

using namespace std;

class OutParser {
private:
    FILE *fout;
    char *buff;
    int sp;

    void write_ch(char ch) {
        if (sp == 50000) {
            fwrite(buff, 1, 50000, fout);
            sp = 0;
            buff[sp++] = ch;
        } else {
            buff[sp++] = ch;
        }
    }


public:
    OutParser(const char* name) {
        fout = fopen(name, "w");
        buff = new char[50000]();
        sp = 0;
    }
    ~OutParser() {
        fwrite(buff, 1, sp, fout);
        fclose(fout);
    }

    OutParser& operator << (int vu32) {
        if (vu32 <= 9) {
            write_ch(vu32 + '0');
        } else {
            (*this) << (vu32 / 10);
            write_ch(vu32 % 10 + '0');
        }
        return *this;
    }

    OutParser& operator << (long long vu64) {
        if (vu64 <= 9) {
            write_ch(vu64 + '0');
        } else {
            (*this) << (vu64 / 10);
            write_ch(vu64 % 10 + '0');
        }
        return *this;
    }

    OutParser& operator << (char ch) {
        write_ch(ch);
        return *this;
    }
    OutParser& operator << (const char *ch) {
        while (*ch) {
            write_ch(*ch);
            ++ch;
        }
        return *this;
    }
};
class InParser {
private:
    FILE *fin;
    char *buff;
    int sp;

    char read_ch() {
        ++sp;
        if (sp == 4096) {
            sp = 0;
            fread(buff, 1, 4096, fin);
        }
        return buff[sp];
    }

public:
    InParser(const char* nume) {
        fin = fopen(nume, "r");
        buff = new char[4096]();
        sp = 4095;
    }

    InParser& operator >> (int &n) {
        char c;
        while (!isdigit(c = read_ch()) && c != '-');
        int sgn = 1;
        if (c == '-') {
            n = 0;
            sgn = -1;
        } else {
            n = c - '0';
        }
        while (isdigit(c = read_ch())) {
            n = 10 * n + c - '0';
        }
        n *= sgn;
        return *this;
    }

    InParser& operator >> (long long &n) {
        char c;
        n = 0;
        while (!isdigit(c = read_ch()) && c != '-');
        long long sgn = 1;
        if (c == '-') {
            n = 0;
            sgn = -1;
        } else {
            n = c - '0';
        }
        while (isdigit(c = read_ch())) {
            n = 10 * n + c - '0';
        }
        n *= sgn;
        return *this;
    }
};
using namespace std;
const int nmax=1e5+3;
bool viz[nmax],grad[nmax];
vector <int> v[nmax];
int n,m,a,b,k,nod;
stack <int> st;
void dfs(int nod)
{
    viz[nod]=1;
    for(int i=0;i<v[nod].size();++i)
    {
        if(!viz[v[nod][i]]) dfs(v[nod][i]);
    }
}
int main()
{
    InParser f ("ciclueuler.in");
    OutParser g("ciclueuler.out");
    f>>n>>m;
    for(int i=1;i<=m;++i)
    {
        f>>a>>b;
        v[a].push_back(b);
        v[b].push_back(a);
        grad[a]^=1;
        grad[b]^=1;
    }
    //dfs(1);
    for(int i=1;i<=n;++i)
    {
        if(!viz[i]||grad[i])
        {
            g<<-1;
            return 0;
        }
    }
    st.push(1);
    while(!st.empty())
    {
        k=st.top();
        if(v[k].size())
        {
            nod=v[k].back();
            v[k].pop_back();
            st.push(nod);
            v[nod].erase(find(v[nod].begin(),v[nod].end(),k));
        }
        else
        {
            g<<k<<' ';
            st.pop();
        }
    }
    return 0;
}