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;
}
void traceBorder( const TWallVertexVector& vb, TIntVector& polygon, TIntVector& ib )
{
static int traceID = 0;
++traceID;
int idx0 = getBorderIndex();
assert( idx0 >= 0 && idx0 < vertexTypes.size() );
ib.resize( 0 );
polygon.resize( 0 );
polygon.reserve( vertices.size()/2 );
TIntVector localPolygon;
localPolygon.reserve( 128 );
TIntVector localIB;
localIB.reserve( 128 );
int idxPrev = idx0;
int idx = idx0;
int debugCounter = 0;
int debugLoopCounter = 0;
do {
localIB.resize( 0 );
bool willFormLoop;
do{
localPolygon.push_back( idx );
borderVertices.erase( idx );
vertexTraceID[idx] = traceID;
assert( ++debugCounter <= vertices.size()*2 );
// Next vertex is the neighbor of current, that is not interior
// and that is not the previous one.
// When there are many possible ones, trace based on angle.
int idxNext = -1;
SVector2 prevToCurr = vb[idx] - vb[idxPrev];
if( prevToCurr.lengthSq() < 1.0e-6f )
prevToCurr.set( -0.01f, -0.01f );
TIntIntsMap::const_iterator it;
it = vertexNexts.find( idx );
assert( it != vertexNexts.end() );
const TIntVector& vnext = it->second;
int n = vnext.size();
float bestAngle = 100.0f;
for( int i = 0; i < n; ++i ) {
int idx1 = vnext[i];
if( idx1 != idxPrev && vertexTypes[idx1] != VTYPE_INTERIOR ) {
//if( idx1 != idxPrev ) {
SVector2 currToNext = vb[idx1] - vb[idx];
float ang = signedAngle2D( prevToCurr, currToNext );
if( ang < bestAngle ) {
bestAngle = ang;
idxNext = idx1;
}
}
}
assert( bestAngle > -4.0f && bestAngle < 4.0f );
assert( idxNext >= 0 );
willFormLoop = (vertexTraceID[idxNext] == traceID);
// Optimization: if best angle is zero, then we're walking
// in a straight line. Optimize out the current vertex.
if( bestAngle == 0.0f && idx != idx0 && !willFormLoop ) {
localPolygon.pop_back();
}
idxPrev = idx;
idx = idxNext;
} while( !willFormLoop );
assert( localPolygon.size() >= 3 );
//if( localPolygon.size() < 3 ) {
// return;
//}
assert( ++debugLoopCounter < vertices.size() );
if( idx == idx0 ) {
// The polygon is simple or we found the last loop.
// Triangulate local and append to results.
triangulator::process( vb, localPolygon, localIB );
polygon.insert( polygon.end(), localPolygon.begin(), localPolygon.end() );
ib.insert( ib.end(), localIB.begin(), localIB.end() );
// We can have separated other loops. Try fetching them as well.
idx0 = getBorderIndex();
if( idx0 == -1 ) {
return;
} else {
localPolygon.resize( 0 );
idxPrev = idx0;
idx = idx0;
}
} else {
// The polygon must be complex, and we just found a closed loop.
// Take only the loop, triangulate it, append to results, continue.
TIntVector::const_iterator itLoopStart =
std::find( localPolygon.begin(), localPolygon.end(), idx );
assert( itLoopStart != localPolygon.end() );
// append to results
TIntVector loopPolygon( itLoopStart, localPolygon.end() );
triangulator::process( vb, loopPolygon, localIB );
polygon.insert( polygon.end(), loopPolygon.begin(), loopPolygon.end() );
ib.insert( ib.end(), localIB.begin(), localIB.end() );
// continue - remove the looped polygon from local
localPolygon.resize( itLoopStart - localPolygon.begin() );
}
} while( true );
}
