n, p, k = map(int, input().split())
INF = float("INF")
dp = [[-INF] * (k + 1) for _ in range(n + 1)]
dp[0][0] = p
for i in range(n):
    t, b = map(int, input().split())
    for j in range(k + 1):
        dp[i + 1][j] = dp[i][j]
    for j in range(k):
        if t == 1:
            v = dp[i][j] + b
        else:
            v = dp[i][j] * 2
        dp[i + 1][j + 1] = max(dp[i + 1][j + 1], v)
        if dp[i + 1][j + 1] >= 10**18:
            exit(print(-1))
print(dp[n][k])