program factory;
  const
    max=10000;
  type
    sz=array[1..2,1..max]of longint;
  var
    f1,f2:text;
    min:longint;
    i,n,s,k:integer;
    a:sz;
    procedure ini;
      begin
        assign(f1,'factory.in');reset(f1);
        assign(f2,'factory.out');rewrite(f2);
        fillchar(a,sizeof(a),0);
        readln(f1,n,s);
        min:=0;
        k:=1;
      end;
    procedure main;
      var
        j:integer;
      begin
        for j:=k to i do if a[1,j]<=a[1,k] then k:=j;
        min:=min+a[1,k]*a[2,i];
        a[1,k]:=a[1,k]+s;
      end;
  begin
    ini;
    for i:=1 to n do begin
      readln(f1,a[1,i],a[2,i]);
      main;
    end;
    writeln(f2,min);
    close(f1);
    close(f2);
  end.