#include<cstdio>
#include<vector>
#include<stack>
using namespace std;
vector< pair<int,int> >L[100100];
stack<int>s;
int n,m,i,j,a,ok,b,p,v[500100],x[100100];
FILE *f,*g;
void dfs(int nod){
    v[nod]=1;
    for(int i=0;i<L[nod].size();i++){
        if( v[ L[nod][i].first ] == 0 )
            dfs( L[nod][i].first );
    }
}
int main(){
    f=fopen("ciclueuler.in","r");
    g=fopen("ciclueuler.out","w");
    fscanf(f,"%d%d",&n,&m);
    for(i=1;i<=m;i++){
        fscanf(f,"%d%d",&a,&b);
        L[a].push_back(make_pair(b,i));
        L[b].push_back(make_pair(a,i));
        x[a]++;
        x[b]++;
    }
    for(i=1;i<=n;i++){
        if(x[i]){
            dfs(i);
            p=i;
            break;
        }
    }
    for(i=1;i<=n;i++){
        if( v[i] == 0 || x[i] % 2 ==1 ){
            fprintf(g,"-1");
            return 0;
        }
        v[i]=0;
    }
    s.push(p);
    ok=1;
    while( ! s.empty() ){
        p=s.top();
        if( x[p]==0 ){
            if(ok==0)
                fprintf(g,"%d ",p);
            ok=0;
            s.pop();
        }
        else{
            while( v[ L[p][ L[p].size()-1 ].second ] ==1 ){
                L[p].erase( L[p].end()-1 );
            }
            v[ L[p][ L[p].size()-1].second ]=1;
            s.push(L[p][ L[p].size()-1 ].first);
            x[p]--;
            x[ L[p] [ L[p].size()-1 ].first]--;
            L[p].erase(L[p].end()-1);
        }
    }



    fclose(f);
    fclose(g);
    return 0;
}