#include<cstdio>
#include<stack>
#include<vector>
using namespace std;
vector< pair<int,int> >L[100100];
stack<int>s;
int n,m,a,b,i,ok,j,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);
            a=i;
            break;
        }
    }
    for(i=1;i<=n;i++){
        if(x[i]%2==1||v[i]==0){
            fprintf(g,"-1");
            return 0;
        }
        v[i]=0;
    }
    s.push(a);
    ok=1;
    while(!s.empty()){
        a=s.top();
        if(x[a]==0){
            if(ok==0)
                fprintf(g,"%d ",a);
            ok=0;
            s.pop();
        }
        else{
            while( v[ L[a][ L[a].size()-1 ].second ] == 1 ){
                L[a].erase(L[a].end()-1);
            }
            v[ L[a][ L[a].size()-1].second ]=1;
            s.push(L[a][ L[a].size()-1 ].first);
            x[a]--;
            x[L[a][ L[a].size()-1 ].first]--;
            L[a].erase(L[a].end()-1);
        }
    }


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