N, P, K = map(int, input().split())

dp = [P] * (K + 1)

for _ in range(N):
    T, B = map(int, input().split())
    if T == 1:
        for i in reversed(range(K)):
            dp[i + 1] = max(dp[i + 1], dp[i] + B)
    else:
        for i in reversed(range(K)):
            dp[i + 1] = max(dp[i + 1], dp[i] * 2)

    if dp[-1] > 1000000000000000000:
        print(-1)
        exit(0)

print(dp[-1])