I don't know why I got WA. Can you let me see ?
Here's my source code.

type
    tab = array [1..202] of longint;

var
   E, XX, YY, Imp: array [1..100] of longint;
   n,Min,Max: longint;

   DX,DY: tab;

   X,Y: array [1..202] of longint;
   nX, nY: longint;

   Re, L, A: longint;


procedure Read_Data;
var
   i: longint;
begin
     read(L,A,n);
     Min := maxint;
     Max := 0;
     for i := 1 to n do begin
       read(Imp[i], E[i],XX[i],YY[i]);
       if Imp[i] < Min then Min := Imp[i];
       if Imp[i] > Max then Max := Imp[i];
       DX[i*2-1] := XX[i];
       DX[i*2] := XX[i]+E[i];
       DY[i*2-1] := YY[i];
       DY[i*2] := YY[i]+E[i];
     end;
     DX[2*n+1] := 1;
     DX[2*n+2] := L+1;
     DY[2*n+1] := 1;
     DY[2*n+2] := L+1;
end;


procedure QSort(l,r: integer; var A: tab);
var
   i,j: integer;
   x,k: longint;
begin
     i := l;     j := r;
     x := A[(l+r) div 2];
     repeat
       while A[i] < x do i := i + 1;
       while x < A[j] do j := j - 1;
       if i <= j then begin
         k := A[i];  A[i] := A[j];  A[j] := k;
         i := i + 1;  j := j - 1;
       end;
     until i > j;
     if i < r then QSort(i,r,A);
     if l < j then QSort(l,j,A);
end;


function Common1(x1,l1, x2,l2: longint): boolean;
begin
     Common1 := true;
     if (x1<=x2) and (x2+l2<=x1+l1) then exit;
     if (x2<=x1) and (x1+l1<=x2+l2) then exit;
     if (x2<x1) and (x1<x2+l2) then exit;
     if (x2<x1+l1) and (x1+l1<x2+l2) then exit;
     Common1 := false;
end;


function Common(x1,y1,l1, x2,y2,l2: longint): boolean;
begin
     Common := Common1(x1,l1,x2,l2) and Common1(y1,l1,y2,l2);
end;


procedure Solve;
var
   i,j,k,h: longint;
begin
     nX := 1;
     X[nX] := DX[1];
     for i := 2 to 2*n+2 do begin
       if DX[i]+A > L+1 then break;
       if DX[i] <> DX[i-1] then begin
         nX := nX+1;
         X[nX] := DX[i];
       end;
     end;

     nY := 1;
     Y[nY] := DY[1];
     for i := 2 to 2*n+2 do begin
       if DY[i]+A > L+1 then break;
       if DY[i] <> DY[i-1] then begin
         nY := nY+1;
         Y[nY] := DY[i];
       end;
     end;

     Re := maxint;
     for i := 1 to nX-1 do
       for j := 1 to nY-1 do begin
         {X[i],Y[j]  left down corner}
         h := Min;
         for k := 1 to n do
           if (h < Imp[k]) and Common(X[i],Y[j],A, XX[k],YY[k],E[k])
                then h := Imp[k];
         if h < Re then Re := h;
         if Re=Min then exit;
       end;
end;


procedure Write_Result;
begin
     if Re > 100 then writeln('IMPOSSIBLE')
       else writeln(Re);
end;


begin
     Read_Data;
     if A<L then begin
       QSort(1,2*n+2, DX);
       QSort(1,2*n+2, DY);
       Solve;
     end else Re := Max;
     Write_Result;
end.