#include <cstdio>
#include <vector>

using namespace std;

const char InFile[]="ciclueuler.in";
const char OutFile[]="ciclueuler.out";
const int MaxN=100111;
const int MaxM=500111;

FILE *fin=fopen(InFile,"r");
FILE *fout=fopen(OutFile,"w");

int N,M,x,y,D[MaxN];
vector<int> G[MaxN],sol,S;

int main()
{
	fscanf(fin,"%d %d",&N,&M);
	for(register int i=1;i<=M;++i)
	{
		fscanf(fin,"%d %d",&x,&y);
		G[x].push_back(y);
		G[y].push_back(x);
		++D[x];
		++D[y];
	}
	fclose(fin);
	
	for(register int i=1;i<=N;++i)
	{
		if(D[i]&1)
		{
			fprintf(fout,"-1");
			return 0;
		}
	}
	
	S.push_back(1);
	while(!S.empty())
	{
		int nod=S.back();
		if(G[nod].size()==0)
		{
			sol.push_back(nod);
			S.pop_back();
		}
		else
		{
			int e=G[nod].back();
			G[nod].pop_back();
			S.push_back(e);
			for(register int i=0;i<G[e].size();++i)
			{
				if(G[e][i]==nod)
				{
					G[e][i]=G[e].back();
					G[e].pop_back();
					break;
				}
			}
		}
	}

	for(register int i=1;i<sol.size();++i)
	{
		fprintf(fout,"%d ",sol[i]);
	}
	fclose(fout);
	return 0;
}