#include<iostream>
#include<algorithm>
#define ll long long
using namespace std;
ll n,m,ans=0,s[100005];
bool cmp(int x,int y){
return x>y;
}
int main(){
cin>>n>>m;
for(int i=1;i<=n;i++){
ll a,b;
cin>>a>>b;
s[i]=a-b;
ans+=a;
}
sort(s****+n+1,cmp);
for(int i=1;i<=n;i++){
if(ans>m){
ans-=s[i];
}
else{
cout<<i-1<<"\n";
return 0;
}
}
cout<<"-1\n";
return 0;
}