freopen(".in","r",stdin);
	freopen(".out","w", stdout);

#include<bits/stdc++.h>
using namespace std;
long long n,sum,a[100005],x,y,s,o;
int main()
{
	cin>>n>>sum;
	for(int i=0;i<n;i++)
	{
		cin>>x>>y;
		a[i]=x-y;
		s+=x;
	}
	sort(a,a+n);
	if(s<=sum)
	{
		cout<<0;
		return 0;
	}
	o++;
	for(int i=n-1;i>=0;i--)
	{
		if(s-a[i]<=sum)
		{
			cout<<o;
			return 0;
		}
		else
		{
			s-=a[i];
			o++;
		}
	}
	cout<<-1;
	return 0;
}