#include <fstream>
#include <vector>
#include <stack>
#define nmax 500100

using namespace std;
ifstream f("ciclueuler.in");
ofstream g("ciclueuler.out");

int N, M, nrInOut[nmax];
bool folosit[nmax];
vector <pair <int, int> > muchi;
vector <int> graf[nmax], Sol;
bool esteInComp[nmax];

void creereVectorPrimaCompConexa(int nod){
    int n2;
    for(int i = 0; i < graf[nod].size(); ++i){
        if(!esteInComp[ n2 = muchi[ graf[nod][i] ].first + muchi[ graf[nod][i] ].second - nod ]){
            esteInComp[n2] = true;
            creereVectorPrimaCompConexa(n2);
        }
    }
}
bool esteConex(){
    creereVectorPrimaCompConexa(1);

    for(int i = 1; i <= N; ++i){
        if(!esteInComp[i])
            return false;
    }

    return true;
}
bool isEuler(){

    for(int i = 1; i <= N; ++i)
        if( !nrInOut[i] || nrInOut[i] % 2 != 0 || !esteConex() )
            return false;
    return true;
}

void euler(int nod){
int i;
        for(i = 0; i < graf[nod].size(); ++i){
            if(! folosit[ graf[nod][i] ]){
                int nod2 = muchi[ graf[nod][i] ].first + muchi[ graf[nod][i] ].second - nod;

                folosit[ graf[nod][i] ] = true;
                euler(nod2);
            }
        }
    Sol.push_back(nod);
}

int main()
{int a, b;
    f>>N>>M;
    muchi.push_back( make_pair(0, 0) );
    for(int i = 1; i <= M; ++i){
        f>>a>>b;
        muchi.push_back( make_pair(a, b) );
        graf[a].push_back(i);

        if(a != b){
            graf[b].push_back(i);
            ++nrInOut[a];
            ++nrInOut[b];
        }

    }

    /*for(int i = 1; i <= N; ++i){
        for(int j = 0; j < graf[i].size(); ++j){
            g<<muchi[ graf[i][j] ].first<<' '<<muchi[ graf[i][j] ].second<<' ';
        }
        g<<'\n';
    }*/

    if( isEuler() ){
        euler(1);
        for(int i = Sol.size() - 1; i > 0; --i)
            g << Sol[i] <<' ';
            g<<'\n';
        return 0;
    }
    g<<-1<<'\n';

    return 0;
}