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

m = 10 ** 18 + 1
dp = [[0 for _ in range(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] = 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), m)
            else:
                dp[i + 1][j + 1] = min(max(dp[i + 1][j + 1], dp[i][j] * 2), m)

print([max(dp[n]), -1][max(dp[n]) == m])