program ex;
type
 ss=array[1..1000000]of longint;
var
 a,f:ss;
 n,k,c:longint;
 f1,f2:text;
 max,min:longint;
procedure init;
 var
  i,j:longint;
 begin
  max:=0;min:=maxlongint;
  assign(f1,'divide.in');
  assign(f2,'divide.out');
  reset(f1);
  rewrite(f2);
  readln(f1,n,k,c);
  for i:=1 to n do
   begin
    read(f1,a[i]);
    if a[i]>max then max:=a[i];
    if a[i]<min then min:=a[i];
   end;
  close(f1);
 end;
procedure main;
 var
  i,j:longint;
  x,y:longint;
 begin
  x:=0;
  y:=0;
  if c*k<c+(max-min)*(max-min) then f[k]:=c*k
                     else f[k]:=c+(max-min)*(max-min);
  for i:=k+1 to n do
   begin
    x:=f[i-1]+c*(i-k);
    y:=f[i-1]+c+(max-min)*(max-min);
    if x<y then f[i]:=x
           else f[i]:=y;
   end;
  writeln(f2,f[n]);
 end;
begin
 init;
 main;
 close(f2);
end.