1 #include<cstdio>
 2 #include<algorithm>
 3 #define ll long long
 4 using namespace std;
 5 ll n,m,cnt,ans,g,l[100010],k;
 6 int main()
 7 {
 8     scanf("%lld%lld%lld",&n,&m,&k); 
 9     for (ll i=1,x,y;i<=n;i++) { scanf("%lld%lld",&x,&y); if (y>=(2*k)) l[++cnt]=x; }    
10     sort(l+1,l+cnt+1);
11     for (ll i=cnt;i>=1;i--) if (g+l[i]<m) g+=l[i],ans++; else { g+=l[i]; ans++; break; }
12      if (g>=m) printf("%lld",ans); else printf("-1"); 
13 }