n,s = map(int,input().split())
a,b = map(int,input().split())
l = []
ans = 0

for i in range(n):
    x = list(map(int,input().split()))
    if x[0] <= a+b:
        l.append(x)

l.sort(key=lambda x:x[1])

i = 0
while 1:
    s -= l[i][1]
    if s>0:
        ans += 1
    else:
        break
    i += 1

print(ans)