program batch;
 const
   maxn = 5000;
 var
  n,s:  longint;
  T,F:              array[0..maxn] of longint;
  opt,sumT,sumF:    array[0..maxn] of int64;

  i,j:      longint;
  tmp,inf:      int64;

begin
  assign(input,'batch.in');  reset(input);
  assign(output,'batch.out'); rewrite(output);
  readln(n);
  readln(s);
  for i :=1 to n do readln(T[i],F[i]);
  for i :=1 to n do sumT[i] :=sumT[i-1] + T[i];
  for i :=1 to n do sumF[i] :=sumF[i-1] + F[i];

  inf :=1; for i :=1 to 16 do inf :=inf *10;
  for i :=1 to n do opt[i] :=Inf;

  for i :=1 to n do
      for j :=0 to i-1 do begin
      tmp :=opt[j] + (s + (sumT[i]-sumT[j])) * (sumF[n]-sumF[j]);
      if tmp <opt[i] then opt[i] :=tmp;
      end;
  writeln(opt[n]);
  close(input); close(output);
end.