CH Round #59 - OrzCC杯NOIP模拟赛day1

program book;
var
  a,f,g:array[0..200001]of qword;
  l,r:array[0..100001]of longint;
  n,i,m:longint; sum,ans:qword;
procedure qsort(l,h:longint);
var i,j,t:longint; m:qword;
begin i:=l; j:=h;
 m:=a[(i+j) div 2];
 repeat
while a[i]<m do inc(i);
while m<a[j] do dec(j);
if i<=j then
  begin   t:=a[i]; a[i]:=a[j]; a[j]:=t;
inc(i); dec(j);  end;  until i>j;
 if i<h then qsort(i,h); if j>l then qsort(l,j);  end;
function make(x:longint):longint;
var l,r,mid,ans:longint;
begin
  l:=1;r:=m;
  while l<=r do
   begin
     mid:=(l+r) div 2;
     if f[mid]<=x then begin ans:=mid; l:=mid+1; end
      else begin r:=mid-1; end;
   end;
  exit(ans);
end;
procedure fry;
var i:longint;
begin
  qsort(1,2*n);
  a[0]:=-1;
  for i:=1 to 2*n do
   if a[i]<>a[i-1] then begin inc(m); f[m]:=a[i]; end;
  for i:=1 to n do
   begin
     l[i]:=make(l[i]); r[i]:=make(r[i]);
   end;
end;
begin
  assign(input,‘book.in‘);
reset(input);
assign(output,‘book.out‘);
rewrite(output);
  readln(n); m:=0;
  for i:=1 to n do
   begin
      readln(l[i],r[i]);
      a[i*2-1]:=l[i];  a[i*2]:=r[i];
   end;
  fry;
  for i:=1 to n do
   begin
     inc(g[l[i]]); dec(g[r[i]+1]);
   end;
  for i:=1 to m do
   begin
     inc(sum,g[i]);
     if sum*f[i]>ans then ans:=sum*f[i];
   end;
  writeln(ans);
  close(input); close(output);
end.