N, P, K = map(int, input().split())
ans = [P] * (K + 1)
inf = 10 ** 20
for _ in range(N) :
	t, b = map(int, input().split())
	for i in range(K, 0, -1) :
		if t == 1 :
			ans[i] = max(ans[i], ans[i - 1] + b)
		else :
			ans[i] = max(ans[i], ans[i - 1] * 2)
		ans[i] = min(inf, ans[i])
print(-1 if ans[K] > 10 ** 18 else ans[K])