I don't understand why my grogram got "WA",please help me.
 Thank you!
Here is my grogram:
const
 inp='';
 maxn=100;

var
 a:array[1..18,1..3]of 0..51;
 t:set of 1..51;
 n,max,ma:integer;

procedure input;
 var
  b:array[1..maxn] of string[20];
  i,j,k,m:integer;
  s:string;
  f:text;
 begin
  fillchar(a,sizeof(a),0);
  assign(f,inp);
  reset(f);
  readln(f,n);
  fillchar(b,sizeof(b),' ');
  m:=0;
  for i:=1 to n do
   begin
    readln(f,s);

    k:=pos(' ',s);
    for j:=1 to m do
     if copy(s,1,k-1)=b[j] then begin a[i,1]:=j;break;end;
    if a[i,1]=0 then begin m:=m+1;a[i,1]:=m;b[m]:=copy(s,1,k-1);end;
    delete(s,1,k);

    k:=pos(' ',s);
    for j:=1 to m-1 do
     if copy(s,1,k-1)=b[j] then begin a[i,2]:=j;break;end;
    if a[i,2]=0 then begin m:=m+1;a[i,2]:=m;b[m]:=copy(s,1,k-1);end;
    delete(s,1,k);

    for j:=1 to m-1 do
     if s=b[j] then begin a[i,3]:=j;break;end;
    if a[i,3]=0 then begin m:=m+1;a[i,3]:=m;b[m]:=s;end;
   end;
  close(f);
 end;

procedure find(i:integer);
 var
  j:integer;
 begin
  for j:=1 to 2 do
   if not(a[i,1] in t)and not(a[i,2] in t)and not(a[i,3] in t) then
    begin
     t:=t+[a[i,1]]+[a[i,2]]+[a[i,3]];
     ma:=ma+1;
     if i<>n then find(i+1) else if ma>max then max:=ma;
     ma:=ma-1;
     t:=t-[a[i,1]]-[a[i,2]]-[a[i,3]];
    end else if i<>n then find(i+1) else if ma>max then max:=ma;
 end;

begin
 input;
 max:=0;ma:=0;
 find(1);
 writeln(max);
end.