function NumberAdd(a, b: string): string;
var i, len: integer;
    p: array of byte;
begin
   if Length(a)>Length(b) then
      len:=Length(a)+1 else
      len:=Length(b)+1;
   while Length(a)<len do
      a:='0'+a;
   while Length(b)<len do
      b:='0'+b;
   SetLength(p, len);
   Result:='';
   for i:=0 to len-1 do
      p[i]:=0;
   for i:=len downto 2 do
   begin
      p[i-1]:=p[i-1]+StrToInt(a[i])+StrToInt(b[i]);
      if p[i-1]>=10 then
      begin
         p[i-2]:=p[i-1] div 10;
         p[i-1]:=p[i-1] mod 10;
      end;
   end;
   for i:=0 to len-1 do
      Result:=Result+IntToStr(p[i]);
   while (Result<>'') and (Result[1]='0') do
      Delete(Result, 1, 1);
end;

function NumberMul(a, b: string): string;
var i, j: integer;
    s: string;
    p: array of byte;
begin
   SetLength(p, Length(a)+Length(b));
   Result:='';
   for i:=Length(a) downto 1 do
   begin
      s:='';
      for j:=0 to Length(a)+Length(b)-1 do
         p[j]:=0;
      for j:=Length(b) downto 1 do
      begin
         p[i+j-1]:=p[i+j-1]+StrToInt(a[i])*StrToInt(b[j]);
         if p[i+j-1]>=10 then
         begin
            p[i+j-2]:=p[i+j-1] div 10;
            p[i+j-1]:=p[i+j-1] mod 10;
         end;
      end;
      for j:=0 to Length(a)+Length(b)-1 do
         s:=s+IntToStr(p[j]);
      while (s<>'') and (s[1]='0') do
         Delete(s, 1, 1);
      Result:=NumberAdd(Result, s);
   end;
end;