program z588;
uses crt;
var n,y,f,s,i:integer;
BEGIN
clrscr;
writeln('vvedite n');
readln(n);
f:=1;
s:=0;
for i:=1 to n do
begin
f:=f*i;
s:=s+f;
end;
writeln(s);
readln;
END.