uses crt;
var n,i,j,kt,s,k,z:longint; a:array[1..1000]of char; t:char;
begin
clrscr;
readln(n);
for i:=1 to n do
begin
read(a[i]);
if i<>n then read(t);
end;
readln;
for i:=1 to n do
begin
kt:=0;
for j:=1 to i-1 do if a[i]=a[j] then kt:=1;
if kt=0 then
for j:=i+1 to n do
begin
k:=1;
for z:=i+1 to j-1 do if a[j]=a[z] then k:=0;
s:=s+k;
end;
end;
writeln(s);
readln
end.