#include<bits/stdc++.h>
using namespace std;
int n,a,s,b,x[100],y[100],max=0;
void dfs(int rest,int  num,int sum){
	if(num==n-1){
		if(sum>max)max=sum;
		return;
	}
	else{
		if(x[i]>a+b)dfs(rest,num+1,sum);
		else if(y[i]>s)dfs(rest,num+1,sum);
		else{
			dfs(rest,num+1,sum);
			dfs(rest-b[i],num+1,)
		} 
	}
}
int main(){
	cin>>n>>s>>a>>b;
	for(int i=0;i<n;i++)
	cin>>x[i]>>y[i];
	int max;
	dfs(s,1,0);
	cout<<max;
	return 0;
}