var n,i,j,aux,nr:longint;
v:array[1..10000] of longint;
f,g:text;
c:char;
begin
assign(f,'litere.in');reset(f);
assign(g,'litere.out');rewrite(g);
read(f,n);
for i:=1 to n do begin
read(f,c);
v[i]:=ord(c);
end;
nr:=0;
for i:=1 to n-1 do
for j:=i+1 to n do
if v[i]>v[j] then begin
aux:=v[i];
v[i]:=v[j];
v[j]:=aux;
inc(nr);
end;
writeln(g,nr);
close(f);
close(g);
end.