program palin;
const
  jx=5000;
var
  a,b,s:array[1..jx]of char;
  max:array[0..jx,0..jx]of integer;
  n,i,j1,j2,maxs:integer;
begin
  assign(input,'palin.in');
  assign(output,'palin.out');
  reset(input);
  rewrite(output);
  readln(n);
  for i:=1 to n do
    read(s[i]);
  fillchar(max,sizeof(max),0);
  max[1,1]:=1;
  maxs:=0;
  for i:=0 to n do
  begin
    for j1:=1 to i do
      a[j1]:=s[i+1-j1];
    for j1:=i+1 to n do
      b[j1-i]:=s[j1];
    for j1:=1 to i do
      for j2:=j1 to n-i+1 do
      begin
        if a[j1]=b[j2] then max[j1,j2]:=max[j1-1,j2-1]+1
        else if max[j1-1,j2-1]>max[j1,j2] then max[j1,j2]:=max[j1-1,j2-1];
      end;
    if (n<>0)and(a[1]<>b[1]) then begin
      if max[i,n-i+1]*2+1>maxs then maxs:=max[i,n-i+1]*2+1;
    end
    else begin
      if max[i,n-i+1]*2>maxs then maxs:=max[i,n-i+1]*2;
    end;
  end;
  writeln(n-maxs);
  close(input);
  close(output);
end.