#include <iostream>
#include <vector>
#include <algorithm>
using namespace std;
typedef long long ll;

int main(){
    ll N, K, L, P;
    cin >> N >> K >> L >> P;
    vector<ll> A(N);
    vector<ll> B(N);
    for (ll i = 0; i < N; i++){
        cin >> A[i] >> B[i];
    }
    ll ans = 0;
    for (ll i = 0; i < (1LL << N); i++){
        ll popcnt = 0;
        ll a = 0;
        ll b = 0;
        for (ll j = 0; j < N; j++){
            if ((i >> j) & 1){
                popcnt++;
                a += A[j];
                b += B[j];
            }
        }
        if (popcnt > K) continue;
        if (a <= L && b >= P) ans++;
    }
    cout << ans << endl;
}