oj

#include<bits/stdc++.h>
using namespace std;
int main(){
priority_queue<int,vector<int>,less<int> > q;
int n,m,sum=0,sum1=0;
cin>>n>>m;
for(int i=0;i<n;i++){
int x,y;
cin>>x>>y;
sum+=x;
sum1+=y;
q.push(x-y);
}
if(sum1>m){
cout<<-1;
return 0;
}
int cnt=0;
while(sum>m){
sum-=q.top();
q.pop();
cnt++;
}
cout<<cnt;
return 0;
}