import sys
input = sys.stdin.readline
N, P, K = map(int, input().split())
TB = [list(map(int, input().split())) for _ in range(N)]
dp = [0 for _ in range(K+1)]
dp[0] = P
for i in range(N):
    ndp = [0 for _ in range(K+1)]
    for j in range(K):
        if dp[j]==0:
            continue
        ndp[j] = max(ndp[j], dp[j])
        t, b = TB[i]
        if t==1:
            ndp[j+1] = max(ndp[j+1], dp[j]+b)
        else:
            ndp[j+1] = max(ndp[j+1], dp[j]*2)
        if ndp[j+1]>10**18:
            print(-1)
            exit()
    dp = ndp
print(dp[K])