fact4.pas

来自「Magio牛的usaco源代码」· PAS 代码 · 共 39 行

{
ID:maigoak1
PROG:fact4
}

program fact4;
const
  mul:array[0..3]of integer=(6,2,4,8);
var
  fin,fout:text;
  last,two:integer;
  n,i,t:integer;
begin
  assign(fin,'fact4.in');
  reset(fin);
  readln(fin,n);
  close(fin);
  assign(fout,'fact4.out');
  rewrite(fout);

  last:=1;two:=0;
  for i:=1 to n do begin
    t:=i;
    while t mod 2=0 do begin
      t:=t div 2;
      inc(two);
    end;
    while t mod 5=0 do begin
      t:=t div 5;
      dec(two);
    end;
    last:=last*t mod 10;
  end;

  if two>0 then last:=last*mul[two mod 4] mod 10;
  writeln(fout,last);
  close(fout);
end.