#include<bits/stdc++.h>
using namespace std;
long long a[100005],b[100005],c[100005];
long long n,t,summ=0,sum=0;
int main(){
	scanf("%lld%lld",&n,&t);
	for(int i=1;i<=n;i++){
		scanf("%lld%lld",&a[i],&b[i]);
		sum+=a[i];
		summ+=b[i];
		c[i]=a[i]-b[i];
	}
	if(summ>t){
		cout<<-1<<"\n";
		return 0;
	}
	if(summ==t){
		cout<<n<<"\n";
		return 0;
	}
	if(sum<=t){
		cout<<0<<"\n";
		return 0;
	}
	long long ans=0;
	sort(c,c+n);
	while(sum>t){
		sum=sum-c[n];
		ans++;
		n--;
	}
	printf("%lld\n",ans);
	return 0;
}