const
  maxn=100000;
var
  a:array[0..maxn] of longint;
  n,l,r,c:longint;

procedure init;
var
  i:longint;
begin
  readln(n,c);
  for i:=1 to n do
    readln(a[i]);
end;

procedure qsort(l,r:longint);
var
  i,j,k:longint;
begin
  if l>=r then exit;
  i:=l;j:=r;
  k:=a[(l+r) div 2];
  repeat
    while
 
 a[i]<k do inc(i);
    while a[j]>k do dec(j);
    if i<=j then
      begin
        a[0]:=a[i];a[i]:=a[j];a[j]:=a[0];
        inc(i);dec(j);
      end;
  until i>j;
  qsort(i,r);qsort(l,j);
end;

function find(x:longint):boolean;
var
  i,j,k:longint;
begin
  k:=1;
  j:=a[1]+x;
  for i:=2 to
 
 n do
    while j<=a[i] do
      begin
        inc(k);
        j:=a[i]+x;
        if k=c then break;
      end;
      if k>=c then exit(true) else exit(false);
end;

begin
  assign(input,'aggr.in'); reset(input);
  assign(output,'aggr.out');rewrite(output);
  init;
  qsort(1,n);
  l:=1;
  r:=(a[n]-a[1
 
]) div (c-1);
  while l<r do
   begin
    if find((l+r) div 2)
      then l:=(l+r) div 2
      else r:=(l+r) div 2;
    if l+1=r then break;
   end;
  if find(r) then writeln(r)
    else writeln(l);
  close(input);close(output);
end.