var v:array[1..10010] of longint;
    n,i,j,aux,rez,k,nr,x,poz:longint;
    c:char;

begin
assign(input,'litere.in');reset(input);
assign(output,'litere.out');rewrite(output);
readln(n);
for i:=1 to n do
        begin
        read(c);
        v[i]:=ord(c)-96;
        end;
for i:=1 to 26 do
        begin
//pozitia adevarata este nr+cate sunt mai mari inainte de pozitia curenta
        x:=0;
        for j:=1 to n do
                begin
                if v[j]=i then
                        begin
                        inc(nr);
                        poz:=nr+x;
                        rez:=rez+poz-nr;
                        end;
                if v[j]>i then
                        inc(x);
                end;
        end;
writeln(rez);
close(input);close(output);
end.