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

#define F first
#define S second
using namespace std;
vector< array<int, 3> > v[100000];
ifstream fin("ciclueuler.in");
ofstream fout("ciclueuler.out");
int ansPos = 0;
int s[100000];
int lolPos[100000];
int ans[500000][2];
void f(int x) {
    for(int i = 0; i < v[x].size(); ++i) {
        if(!v[x][i][2]) {
            v[x][i][2] = 1;
            v[v[x][i][0]][v[x][i][1]][2] = 1;
            f(v[x][i][0]);
        }
    }
    ans[ansPos][0] = x;
    ++ansPos;
}
int main() {
    ios_base::sync_with_stdio(0);
    int n,m;
    fin>>n>>m;
    for(int i =0; i < m; ++i) {
        fin>>ans[ansPos][0]>>ans[ansPos][1];
        --ans[ansPos][0];
        --ans[ansPos][1];
        ++s[ans[ansPos][0]];
        ++s[ans[ansPos][1]];
        ++ansPos;
    }
    for(int i = 0; i < n; ++i) {
        v[i].resize(s[i]);
    }

    for(int i = 0; i < m; ++i) {
        int a = ans[i][0];
        int b = ans[i][1];
        array<int, 3> ar;
        if(a == b) {
            //v[a].push_back(make_pair(b, make_pair(v[b].size()+1, 0)));
            //v[b].push_back(make_pair(a, make_pair(v[a].size()-1, 0))); 
            ar[0] = b;
            ar[1] = lolPos[b]+1;
            ar[2] = 0;

            v[a][lolPos[a]] = ar;
            ++lolPos[a];
            ar[0] = b;
            ar[1] = lolPos[b]-1;
            ar[2] = 0;
            v[b][lolPos[b]] = ar; 
            ++lolPos[b];
        }
        else {
            ar[0] = b;
            ar[1] = lolPos[b];
            ar[2] = 0;
            v[a][lolPos[a]] = ar;
            ++lolPos[a];
            ar[0] = a;
            ar[1] = lolPos[a]-1;
            ar[2] = 0;
            v[b][lolPos[b]] = ar; 
            ++lolPos[b];
        }
    }
    ansPos = 0;
    /*
    for(int i =0; i < n; ++i) {
        for(int j = 0; j < v[i].size(); ++j) {
            fout<<v[i][j].F+1<<' '<<v[i][j].S.F<<'*';
        }
        fout<<'\n';
    }

    */
    for(int i =0 ; i < n; ++i) {
        if(v[i].size()&1) {
            fout<<-1<<'\n';
            return 0;
        }
    }
    f(0);
    for(int i = 0; i < ansPos; ++i) {
        fout<<ans[i][0]+1<<' ';
    }
    fout<<'\n';
}