const
  maxn=100000000000000000;

var
  i,j:longint;
  n,k,c,max,min:int64;
  a,f:Array[0..100000]of int64;

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


begin
  assign(input,'dividea.in'); reset(input);
  assign(output,'dividea.out'); rewrite(output);
  readln(n,k,c);
  for i:=1 to n do read(a[i]);
  sort(1,n);
  f[1]:=c;
  for i:=2 to n do
  begin
    f[i]:=maxn;
    for j:=i-k+1 downto 1 do
    begin
      if f[j-1]+c+sqr(a[i]-a[j])<f[i] then f[i]:=f[j-1]+c+sqr(a[i]-a[j]);
    end;
  end;
  writeln(f[n]);
  close(input);
  close(output);
end.