#include <algorithm>
#include <fstream>
#include <vector>
#include <queue>

typedef unsigned int uint;

using namespace std;

int gr[100001];
int c[500003];
int ce[500005];
vector<int> a[100001];
//int viz[100001];
queue <int> Q;
int p = 1, u = 1, nr,k;

void ciclu(int x);
void inser();
void df(int k);
ifstream in("ciclueuler.in");
	ofstream out("ciclueuler.out");
int main()
{
	
	
	int N, M;
	in >> N >> M;

	for (int i = 1; i <= M; i++)
	{
		int x, y;
		in >> x >> y;
		
		a[x].push_back(y);
		a[y].push_back(x);
		
		gr[x]++;
		gr[y]++;
	}
	
	//df(1);
	
	for (int i = 1; i <= N; i++)
		if (gr[i] % 2 )
		{
			out << -1;
			return 0;
		}
	
	//ce[1] = 1;
	u=0;c[u]=1;k=0;
do	
	{
		if (gr[c[u]] > 0)
		{
			ciclu(c[u]);
			//inser();
			
			//u += nr - 1;
		}
		else{
			ce[++k]=c[u];u--;}
	}while (u>0);
	if(k!=M){out << -1;
			return 0;}
	for (int i = 1; i <= k; i++)
		out << ce[i] << ' ';
}

void ciclu(int x)
{
	//nr = 1;
	//c[1] = x;
	
	bool ok = true;
	int nr=x;
	do
	{
		for (int i = 0; (size_t) i < a[x].size() && ok; i++)
		{
			
				u++;
				c[u] = a[x][i];
				
				gr[a[x][i]]--;
				gr[x]--;
				
				int z = a[x][i];
				
				vector<int>::iterator j = find(a[z].begin(), a[z].end(), x);
				a[z].erase(j);
				
				a[x].erase(a[x].begin());
				
				x = z;
				
				break;
			}
			
	} while (x!=nr);
	ce[++k]=x;
u--;	
}

/*void inser()
{
	for (int i = u; i >= p + 1; i--)
		ce[i + nr -1] = ce[i];
	
	for (int i = 2; i <= nr; i++)
		ce[p + i - 1] = c[i];
}

void df(int k)
{   int s , v;
   Q.push(1),viz[1]=true;
    while(!Q.empty() ) {
        v = Q.front(),Q.pop(),viz[v] = true;
       for(s=0;(size_t)s<a[v].size();s++)
            if ( !viz[a[v][s]] )
                Q.push(a[v][s]);
	}
}
/*void df(int k)
{
	viz[k] = 1;
	
	for (int i = 0; (size_t)i < a[k].size(); i++)
		if (viz[a[k][i]] == 0)
			df(a[k][i]);
}*/