n, p, k = map(int, input().split())
dp = [0] * (k + 1)
dp[0] = p
for _ in range(n):
    t, b = map(int, input().split())
    for i in range(k, 0, -1):
        if dp[i - 1] == 0:
            continue
        if t == 1:
            dp[i] = max(dp[i], dp[i - 1] + b)
        else:
            dp[i] = max(dp[i], dp[i - 1] * 2)

        if dp[i] > 10**18:
            print(-1)
            exit()

print(dp[k])