/* @JUDGE_ID: 32472GK 1097 C++ */
#include <iostream>
#include <vector>
#include <map>
#include <set>
#include <algorithm>
using namespace std;

struct area   { int c,x,y,l; };
struct c_rect { int c,x1,y1,x2,y2; };

void calc_costa( const vector<area>& areas, int A, vector<area>& careas )
{
  careas = areas;
  for(int i=0; i!=areas.size(); ++i)
    careas[i].x -= (A-1),
    careas[i].y -= (A-1),
    careas[i].l += (A-1);
}

void remap( map<int,int>& fx, map<int,int>& fy, const vector<area>& careas, vector<c_rect>& ans )
{
  ans.clear();
  for(int i=0; i!=careas.size(); ++i)
    {
      int x1 = careas[i].x;
      int y1 = careas[i].y;
      int x2 = careas[i].x + careas[i].l;
      int y2 = careas[i].y + careas[i].l;
      int im = careas[i].c;
      c_rect cr = {im, fx[x1], fy[y1], fx[x2], fy[y2]};
      ans.push_back(cr);
    }
}


int main()
{
  // input areas
  int L,A,M;
  cin >> L >> A >> M;
  vector<area> as;
  for(int i=0; i!=M; ++i)
    {
      int im,l,x,y;
      cin >> im >> l >> x >> y;
      area a = {im,x,y,l};
      as.push_back( a );
    }

  // calc careas
  vector<area> careas;
  calc_costa( as, A, careas );

  // coordinate remapping
  set<int> xs, ys;
  xs.insert(1); xs.insert(1+L); xs.insert(1+L-A);
  ys.insert(1); ys.insert(1+L); ys.insert(1+L-A);
  for(int i=0; i!=careas.size(); ++i)
    {
      xs.insert( careas[i].x );
      xs.insert( careas[i].x + careas[i].l );
      ys.insert( careas[i].y );
      ys.insert( careas[i].y + careas[i].l );
    }

  map<int, int> fx, fy;
  int cnt=0; for(set<int>::iterator it=xs.begin(); it!=xs.end(); ++it) { fx[*it] = cnt++; }
      cnt=0; for(set<int>::iterator it=ys.begin(); it!=ys.end(); ++it) { fy[*it] = cnt++; }

  // remap
  vector<c_rect> crs;
  remap(fx,fy,careas,crs);

  // fill mesh
  static int mesh[201][201];
  for(int i=0; i!=200; ++i)
    for(int j=0; j!=200; ++j)
      mesh[i][j] = 1;
  for(int i=0; i!=crs.size(); ++i)
    {
      c_rect& cr = crs[i];
      for(int x=cr.x1; x<cr.x2; ++x)
        for(int y=cr.y1; y<cr.y2; ++y)
          mesh[x][y] = max<int>( mesh[x][y], cr.c );
    }

  // search minimum
  int minC = 255;
  int Xmin=fx[1], Ymin=fy[1], Xmax=fx[1+L-A], Ymax=fy[1+L-A];
  for(int x=Xmin; x<=Xmax; ++x)
    for(int y=Ymin; y<=Ymax; ++y)
      minC = min<int>( minC, mesh[x][y] );

  // answer
  if( minC > 100 ) cout << "IMPOSSIBLE" << endl;
  else             cout << minC << endl;
  return 0;
}