from collections import defaultdict
import bisect

class BIT:
    def __init__(self, n):
        self.size = n
        self.list = [0] * (n + 1)
    
    def add(self, i, x):
        if i == 0:
            return
        while i <= self.size:
            self.list[i] += x
            i += (i & -i)
    
    def sum(self, i):
        if i == 0:
            return 0
        ret = 0
        while i > 0:
            ret += self.list[i]
            i -= (i & -i)
        return ret


def MakeList(lst):
    ret = [[] for _ in range(len(lst) + 1)]
    for i in range(1 << (len(lst))):
        popcnt = 0
        b = 0
        a = 0
        for j in range(len(lst)):
            if ((i >> j) & 1):
                popcnt += 1
                b += lst[j][0]
                a += lst[j][1]
        ret[popcnt].append([b, a])
    for i in range(len(lst) + 1):
        ret[i].sort()
    return ret

def MakeUniqueA(lst):
    new_lst = []
    for i in range(len(lst)):
        for j in range(len(lst[i])):
            new_lst.append(lst[i][j][1])
    ret = list(set(new_lst))
    ret.sort()
    return ret

N, K, L, P = map(int, input().split())
former = []
latter = []
for i in range(N):
    a, b = map(int, input().split())
    if i < N // 2:
        former.append([b, a])
    else:
        latter.append([b, a])

former_lst = MakeList(former)
latter_lst = MakeList(latter)

former_a = MakeUniqueA(former_lst)
latter_a = MakeUniqueA(latter_lst)

#print(former_a)
#print(latter_a)

d_former = defaultdict(int)
d_latter = defaultdict(int)

for i in range(len(former_a)):
    d_former[former_a[i]] = i + 1
for i in range(len(latter_a)):
    d_latter[latter_a[i]] = i + 1

idx = [0 for _ in range(len(former_a))]
for i in range(len(former_a)):
    if former_a[i] + latter_a[len(latter_a) - 1] <= L:
        idx[i] = len(latter_a)
    elif former_a[i] + latter_a[0] > L:
        idx[i] = 0
    else:
        idx[i] = bisect.bisect_right(latter_a, L - former_a[i])

bit = BIT((1 << 18) + 1)
ans = 0

for i in range(len(former_lst)):
    for j in range(len(latter_lst)):
        if i + j > K:
            continue
        now = len(latter_lst[j]) - 1
        for k in range(len(former_lst[i])):
            while now >= 0:
                if former_lst[i][k][0] + latter_lst[j][now][0] >= P:
                    bit.add(d_latter[latter_lst[j][now][1]], 1)
                    now -= 1
                else:
                    break
            sm = bit.sum(idx[d_former[former_lst[i][k][1]] - 1])
            ans += sm
        for k in range(now + 1, len(latter_lst[j])):
            bit.add(d_latter[latter_lst[j][k][1]], -1)

print(ans)