void addPolygon( const TIntVector& ib )
{
++polygonCount;
TIntVector::const_iterator vit, vitEnd = ib.end();
for( vit = ib.begin(); vit != vitEnd; ++vit ) {
int idx = *vit;
assert( idx >= 0 && idx < vertexUseCount.size() );
vertices.insert( idx );
++vertexUseCount[idx];
int idxNext = (vit==vitEnd-1) ? ib.front() : *(vit+1);
int idxPrev = (vit==ib.begin()) ? ib.back() : *(vit-1);
vertexNexts[idx].push_back( idxNext );
vertexPrevs[idx].push_back( idxPrev );
}
}
int main()
{
#ifndef ONLINE_JUDGE
ifstream fIn("input.txt");
cin.rdbuf( fIn.rdbuf() );
#endif
int n;
int m;
cin >> n >> m;
TBoolVector dummy(2*n, false);
TMatrix g(2*n, dummy);
for (int i = 0; i < m; ++i)
{
int a;
int b;
cin >> a >> b;
--a;
--b;
g[a][b] = true;
g[b][a] = true;
}
for (int i = 0; i < 2 * n; ++i)
{
g[i][i] = true;
}
TIntVector s;
s.push_back(0);
int next = 1;
do
{
int i = next;
for (; i < 2 * n; ++i)
{
int j = 0;
while (j < s.size() && !g[s[j]][i])
{
++j;
}
if (j == s.size())
{
break;
}
}
if (i == 2 * n)
{
next = s.back() + 1;
s.pop_back();
}
else
{
next = 1;
s.push_back(i);
}
} while (!s.empty() && s.size() != n);
if (s.size() == n)
{
for (int i = 0; i < 2 * n; ++i)
{
if (find(s.begin(), s.end(), i) != s.end())
{
cout << i + 1 << " ";
}
}
cout << endl;
for (int i = 0; i < 2 * n; ++i)
{
if (find(s.begin(), s.end(), i) == s.end())
{
cout << i + 1 << " ";
}
}
cout << endl;
}
else
{
cout << "IMPOSSIBLE\n";
}
return 0;
}
