I don't understand why my program get WA.
Please, help me!!!!!!!!!!!!!!!!!

Const
  f1=0;
  f2=2 shl 15-1;
  dp:Array[1..4]Of Integer=(-4,-1,1,4);

Var
  v,ykw,ykr:Integer;
  Og:Array[1..f2]Of Integer;
  Mv:Array[0..f2]Of Integer;
  b:Boolean;

Procedure Init;
Begin

End;

Procedure ReadData;
Var
  t,i,j:Integer;
  ch:Char;
Begin
  v:=0;t:=0;
  For i:=1 To 4 Do Begin
    For j:=1 To 4 Do Begin
      Inc(t);
      Read(ch);
      If ch='w' Then If t=1 Then v:=1 Else v:=v Xor (2 shl (t-2));
    End;
    ReadLn;
  End;
End;

Function GetNew(p:Integer):Integer;
Var
  i,j,new,np:Integer;
Begin
  If p=1 then new:=v Xor 1 Else new:=v Xor (2 shl(p-2));
  For i:=1 To 4 Do Begin
    np:=p+dp[i];
    If (np<1) Or (np>16) Then Continue;
    If np=1 Then new:=new Xor 1
    Else new:=new Xor (2 shl (np-2));
  End;
  GetNew:=new;
End;

Procedure Solve;
Var
  i,j:Integer;
Begin
  FillChar(Og,SizeOf(Og),0);ykw:=0;ykr:=0;
  FillChar(Mv,SizeOf(Mv),0);Mv[v]:=1;
  Inc(ykw);Og[ykw]:=v;
  b:=True;
  If (v=f1) Or (v=f2) Then Exit;
  While ykr<ykw Do Begin
    Inc(ykr);v:=Og[ykr];
    For i:=1 To 16 Do Begin
      j:=GetNew(i);
      If Mv[j]=0 Then Begin
        Inc(ykw);Og[ykw]:=j;
        Mv[j]:=Mv[v]+1;
        If (j=f1) Or (j=f2) Then Exit;
      End;
    End;
  End;
  b:=False;
End;

Procedure OutData;
Begin
  If Not b Then Write('Impossible') Else Write(Mv[Og[ykw]]-1);
End;

Begin
  Init;
  ReadData;
  Solve;
  OutData;
End.