---

n = int(input())
a = []
for i in range(n):
t, c = map(int, input().splitQ)
a. append((t, c))
T = int (input())
a. sort(key=lambda x: (x[1] / x[o], -x[o]), reverse=True)
ans
= 0
for t, c in a:
if T >= t:
T -= t ans += c
print(ans)