var
a,s:real;
n:integer;
begin
writeln('a*(a+1)*...*(a+n-1)');
write('a: '); readln(a);
write('n: '); readln(n);
s:=1;
repeat
s:=s*(a+n-1);
dec(n);
until n=0;
writeln(s);
end.
