var a:array[1..10000] of char;
b:array[1..10000] of byte;
nr,n,i,j:integer;
f,g:text;
begin
assign(f,'litere.in');reset(f);
assign(g,'litere.out');rewrite(g);
readln(f,n);
for i:=1 to n do
read(f,a[i]);
for i:=1 to n do
b[i]:=(ord(a[i]));
for i:=2 to n do
begin
for j:=i-1 downto 1 do
if b[i]<b[j] then inc(nr);
end;
write(g,nr);
close(f);
close(g);
end.