program EmberAsh;
var
s1,s2:ansistring;
i,j,ss,n,ember:longint;
f:array[0..10000,0..10000]of longint;

function max(a,b:longint):longint;
begin
if a>b then max:=a
  else
  max:=b;
end;

BEGIN
assign(input,'palin.in');reset(input);
assign(output,'palin.out');rewrite(output);
readln(ss);
readln(s1);
for i:=ss downto 1 do
  s2:=s2+s1[i];
for i:=1 to ss do
  for j:=1 to ss do
    begin
    if s1[i]=s2[j] then
      f[i,j]:=f[i-1,j-1]+1
      else
      f[i,j]:=max(f[i-1,j],f[i,j-1]);
end;
ember:=ss-f[ss,ss];
writeln(ember);
close(input);close(output);
END.