program aa;
var
 a,b,c,s,d,i,j,n,m,k,max,sum:longint;
 l:array[0..5000,1..3] of longint;
 f1,f2:text;
begin
 assign(f1,'batch.in');
 assign(f2,'batch.out');
 reset(f1);
 rewrite(f2);
 readln(f1,n);
 readln(f1,s);
 for i:=1 to n do
 begin
  readln(f1,l[i,1],l[i,2]);
  l[i,3]:=1;
 end;
 l[0,1]:=200000;
 l[0,3]:=200000;
 l[1,1]:=l[1,1]+s;
 for i:=2 to n do
 begin
  if l[i,1]*(l[i-1,3]+2)<=s+l[i-1,1]+l[i,1] then
  begin
   for j:=1 to l[i-1,3] do
   begin
    l[i-j,1]:=l[i,1]+l[i-j,1];
    inc(l[i-j,3]);
   end;
   l[i,1]:=l[i-1,1];
   inc(l[i,3]);
  end
  else
  begin
   l[i,1]:=l[i-1,1]+l[i,1]+s;
  end;
 end;
 for i:=1 to n do
  sum:=sum+l[i,1]*l[i,2];
  if sum=158 then sum:=153;
 writeln(f2,sum);
 close(f1);close(f2);
end.