program cch(input,output);
var
 i,n,ans,j:integer;
 a,b:array[1..5000] of char;
 f:array[0..5000,0..5000] of integer;

function max(x,y:integer):integer;
begin
 if x>y then exit(x)
        else exit(y);
end;

begin
 assign(input,'palin.in');
 assign(output,'palin.out');
 reset(input);
 rewrite(output);
 readln(n);
 for i:=1 to n do read(a[i]);
 for i:=1 to n do
  b[i]:=a[n-i+1];
 f[0,0]:=0; f[0,1]:=0; f[1,0]:=0;
 for i:=1 to n do
  for j:=1 to n do
   if a[i]=b[j] then f[i,j]:=f[i-1,j-1]+1
                else f[i,j]:=max(f[i,j-1],f[i-1,j]);
 ans:=n-f[n,n];
 write(ans);
 close(input);
 close(output);
end.