#include <bits/stdc++.h>
#define int long long
using namespace std;
map<int,int> mp;
vector<int> g;
int n,a,b,ans=0;
int u,v;

signed main(){
	freopen("Compatible.in","r",stdin);
	freopen("Compatible.out","w",stdout);
	scanf("%lld%lld%lld",&n,&a,&b); 
	for(int i=1;i<=n;i++){
		scanf("%lld%lld",&u,&v);
		mp[v]=u;
		g.push_back(v);
	}
	sort(g.begin(),g.end());
	for(auto x:g){
		int pa=a-x,pb=b-x;
		if(mp[pb]>0 && pb>=0){
			if(pb==x){	
				ans+=mp[pb]/2,mp[pb]%=2;
			} 
			else{
				int minn=min(mp[x],mp[pb]);
				ans+=minn;
				mp[x]-=minn;
				mp[pb]-=minn;
			}
		}
		if(mp[pa]>0 && pa>=0){
			if(pa==x){
				ans+=mp[pa]/2,mp[pa]%=2;
			}
			else{
				int minn=min(mp[x],mp[pa]);
				ans+=minn;
				mp[x]-=minn;
				mp[pa]-=minn;
			}
		}
	}
	cout<<ans;
	return 0;
}