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