#include<bits/stdc++.h>
using namespace std;
struct cow
{
    int n,d;
}c[200010];

bool cmp(cow x,cow y)
{
    return x.d<y.d;
}
int main()
{
    freopen("Compatible.in","r",stdin);
    freopen("Compatible.out","w",stdout);
    int n,a,b,d,ans,i,j;
    cin>>n>>a>>b;
    ans=0;
    for(i=1;i<=n;i++)
    {
        cin>>c[i].n>>c[i].d;
    }
    sort(c+1,c+n+1,cmp);
    for(i=1;i<=n;i++)
    {
        for(j=i;j<=n&&c[i].n!=0&&c[i].d+c[j].d<=b;j++)
        {
            if(c[j].n==0)
            {
                continue;
            }
            if(c[i].d+c[j].d==a||c[i].d+c[j].d==b)
            {
                d=min(c[i].n,c[j].n);
                c[i].n=c[i].n-d;
                c[j].n=c[j].n-d;
                if(i==j)
                {
                    d=d/2;
                }
                ans=ans+d;
            }
        }
    }
    cout<<ans;
    return 0;
}