#include <cstdio>
#include <cstdlib>
#include <vector>
#include <stack>
using namespace std;
const int NMAX = 100010;
int N, M, X, Y, Ans[5 * NMAX];
vector<int> G[NMAX];
void Erase(int Node, int Son)
{
for(vector<int> :: iterator it = G[Node].begin(); it != G[Node].end(); ++ it)
if(*it == Son)
{
G[Node].erase(it);
return ;
}
}
void Euler(int Node)
{
stack<int> S;
S.push(Node);
while(!S.empty())
{
int Node = S.top();
if(G[Node].size())
{
int Son = G[Node].back(); G[Node].pop_back();
Erase(Son, Node);
S.push(Son);
}else
{
S.pop();
Ans[++ Ans[0]] = Node;
}
}
}
int main()
{
freopen("ciclueuler.in", "r", stdin);
freopen("ciclueuler.out", "w", stdout);
scanf("%i %i", &N, &M);
for(int i = 1; i <= M; ++ i)
{
scanf("%i %i", &X, &Y);
G[X].push_back(Y);
G[Y].push_back(X);
}
for(int i = 1; i <= N; ++ i)
if(G[i].size() % 2)
{
printf("-1\n");
return 0;
}
Euler(1);
for(int i = 1; i < Ans[0]; ++ i) printf("%i ", Ans[i]);
}