MAX = 10 ** 18
n,p,k = map(int, input().split())
a = [list(map(int, input().split())) for i in range(n)]
ans = p
for BIT in range(2 ** n):
	bit = bin(BIT)[2:].zfill(n)
	if bit.count("1") != k:
		continue
	cnt = p
	for i in range(n):
		if bit[i] == "1":
			if a[i][0] == 1:
				cnt += a[i][1]
			else:
				cnt *= 2
		if cnt > MAX:
			print(-1)
			exit()
	ans = max(ans, cnt)
print(ans)