#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[100100],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;
		}
	}
	for(i=1;i<=n;i++){
		if( v[i] == 0 || x[i] % 2 ==1 ){
			fprintf(g,"-1");
			return 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;
}