var a:array[1..10003] of char;
    aux:char;
    nr,n,i,j,p:integer;
    f,g:text;
    ok:boolean;
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]);
nr:=0;
for i:=2 to n do begin
    aux:=a[i];
    j:=i-1;
    ok:=false;
    while (j>=1) and (not ok) do
          if aux<a[j] then begin
          a[j+1]:=a[j];j:=j-1;inc(nr); end
    else ok:=true;
    a[j+1]:=aux;
end;
writeln(g,nr);close(g);
end.