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