Program gutui;
 var a,b,n,h,u,i,sum,j,b1:longint;
     s:array [0..100000] of longint;
     fi,fo:text;
begin
 assign(fi,'gutui.in');
  assign(fo,'gutui.out');
 reset(fi); rewrite(fo);
 readln(fi,n,h,u);
  for i:=1 to n do begin
                   readln(fi,a,b);
                    j:=trunc((h-a)/(u));
                   while j>0 do begin
                    if s[j]=0 then begin s[j]:=b; sum:=sum+b; j:=-1 end
                     else begin
                          if s[j]<b then begin b1:=s[j]; s[j]:=b; b:=b1; sum:=sum+s[j]-b; end;
                     end;
                     dec(j);
                    end;
                   end;
  write(fo,sum);
 close(fo);
end.