錯位排列數列
0,1,2,9,44,265,....
遞推公式祥見代碼；
提交時，記得壹定要把文件名改為monkey.pas
program liuke_cuopai;
var
i,k,a,b,c:longint;
begin
assign(input,'monkey.in');
assign(output,'monkey.out');
reset(input);
rewrite(output);
readln(k);
a:=0;
b:=1;
for i:=3 to k do
begin
c:=(a+b)*(i-1);
a:=b;
b:=c;
end;
if k=1 then writeln(a) else if k=2 then writeln(b) else
writeln(c);
close(input);
close(output);
end.