var
  n,k,h,i,j,t:longint;
  s:qword;
begin
  readln(n,k,h);
  s:=1;
  for i:=n-k+1 to n do s:=s*i;
  for i:=1 to h do begin
    readln(t);
    for j:=2 to t do s:=s div j
  end;
  for i:=n-k+1 to n do s:=s*i;
  write(s)
end.

典型的基础排列组合