MAX = 10 ** 18 + 1

n,p,k = map(int, input().split())

dp = [[0 for i in range(k + 1)] for i in range(n + 1)]
dp[0][0] = p
# dp[i][j] = i 番目のエンブレムまで使えて j 種類装備しているときの最大攻撃力

for i in range(n):
	t,b = map(int, input().split())
	for j in range(k + 1):
		dp[i + 1][j] = max(dp[i + 1][j], dp[i][j])
		if j != k:
			if t == 1:
				dp[i + 1][j + 1] = min(max(dp[i + 1][j + 1], dp[i][j] + b), MAX)
			else:
				dp[i + 1][j + 1] = min(max(dp[i + 1][j + 1], dp[i][j] * 2), MAX)
print([max(dp[n]), -1][max(dp[n]) == MAX])