#include <iostream>

 #include <cstring>

 #include <string>

 #include <map>

 #include <set>

 #include <algorithm>

 #include <fstream>

 #include <cstdio>

 #include <cmath>

 #include <stack>

 #include <queue>

 using namespace std;

 const double Pi=3.14159265358979323846;

 typedef long long ll;

 const int MAXN=+;

 const int dx[]={,,,,-};

 const int dy[]={,-,,,};

 const int INF = 0x3f3f3f3f;

 const int NINF = 0xc0c0c0c0;

 const ll mod=1e9+;

 struct  node{

     int p,d;

 }a[MAXN];

 bool cmp(node a,node b)

 {

     return a.d>b.d;

 }

 int main()

 {

     int n;scanf("%d",&n);

     for(int i=;i<=n;i++)

     {

         scanf("%d%d",&a[i].d,&a[i].p);

     }

     int L,P;

     scanf("%d%d",&L,&P);

     for(int i=;i<=n;i++)

     {

         a[i].d=L-a[i].d;

     }

     sort(a+,a+n+,cmp);

     /*for(int i=1;i<=n;i++)

     {

         cout <<a[i].d<<endl;

     }*/

     int ans=;

     priority_queue <int> pque;

     if(n==&&P-L<)

     {

         puts("-1");

         return ;

     }

     for(int i=n;i>=;i--)

     {

         int dis=a[i].d-a[i+].d;

         if(dis>P)

         {

             while(dis>P&&!pque.empty())

             {

                 P+=pque.top();

                 pque.pop();

                 ans++;

             }

             if(dis>P)

             {

                 puts("-1");

                 return ;

             }else

             {

                 P=P-dis;

             }

         }

         else

         {

             P=P-dis;

         }

         pque.push(a[i].p);

     }

     int l=L-a[].d;

     while(!pque.empty()&&P<l)

     {

         P+=pque.top();

         ans++;

         pque.pop();

     }

     if(P<l) puts("-1");

         else printf("%d\n",ans);

     return ;

  }