2
100 0
1000 100

0

对于最优方案：

因为F(N)-（w1+w2+..wn-1)<F(1)-(w2+...+wn-1+wn)

化简得  F(n)+wn<F1+w1

调整ing。。。

也就是说对于最优方案有 Fi+wi<Fi-1+wi-1

Program block;
uses math;
const
   maxn=50000;
var
   n,i,j,ans,totw:longint;
   w,f:array[1..maxn] of longint;

procedure qsort(l,r:longint);
var
   i,j,m,p:longint;
begin
   i:=l;
   j:=r;
   m:=w[(i+j) div 2]+f[(i+j) div 2];
   repeat
      while (w[i]+f[i]<m) do inc(i);
      while (w[j]+f[j]>m) do dec(j);
      if i<=j then
      begin
         p:=w[i];w[i]:=w[j];w[j]:=p;
         p:=f[i];f[i]:=f[j];f[j]:=p;
         inc(i);dec(j);
      end;
   until i>j;
   if (l<j) then qsort(l,j);
   if (i<r) then qsort(i,r);
end;
begin
   read(n);
   for i:=1 to n do
   begin
      read(w[i],f[i]);
   end;
   qsort(1,n);
   ans:=-f[1];
   totw:=0;
   for i:=1 to n do
   begin
      ans:=max(ans,totw-f[i]);
      inc(totw,w[i]);

   end;
   writeln(ans);

end.