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