记录编号	18435	评测结果	AAAAAAAAAA
题目名称	越狱	最终得分	100
用户昵称	ybh	是否通过	通过
代码语言	Pascal	运行时间	1.505 s
提交时间	2010-09-14 20:11:23	内存使用	0.23 MiB

program prisonbreak;
var
  a,b:array[0..10000] of longint;
  f:array[0..10000] of longint;
  n,i,j:longint;
  bool:boolean;

procedure sort(l,r:longint);
var
  i,j,x,y:longint;
begin
  i:=l; j:=r;
  x:=a[(l+r) div 2];
  repeat
    while a[i]<x do inc(i);
    while x<a[j] do dec(j);
    if not(i>j) then
    begin
      y:=a[i]; a[i]:=a[j]; a[j]:=y;
      y:=b[i]; b[i]:=b[j]; b[j]:=y;
      i:=i+1; j:=j-1;
    end;
  until i>j;
  if l<j then sort(l,j);
  if i<r then sort(i,r);
end;

begin
  assign(input,'prisonbreak.in');
  reset(input);
  assign(output,'prisonbreak.out');
  rewrite(output);

  readln(n);
  for i:=1 to n do
    readln(a[i],b[i]);
  readln(a[0],b[0]);
  for i:=1 to n do
    a[i]:=a[0]-a[i];

  sort(1,n);

  fillchar(f,sizeof(f),0);
  f[0]:=b[0];
  for i:=1 to n do
    for j:=i downto 1 do
      if f[j-1]>=a[i] then
      begin
        if f[j-1]+b[i]>f[j]
          then f[j]:=f[j-1]+b[i]
      end
      else break;

  bool:=true;
  for i:=0 to n do
    if f[i]>=a[0] then
    begin
      writeln(i);
      bool:=false;
      break
    end;
  if bool then writeln(-1);

  close(input);
  close(output);
end.