N,P,K = map(int,input().split())
TB = [list(map(int,input().split()))for _ in range(N)]

dp=[[0]*(K+1)for i in range(N+1)]
for i in range(N+1):
    dp[i][0]=P

for i in range(N):
    if TB[i][0]==1:
        for j in range(K):
            if dp[i][j]>0:
                dp[i+1][j+1]=max(dp[i][j+1],dp[i][j]+TB[i][1])
    else:
        for j in range(K):
            if dp[i][j]>0:
                dp[i+1][j+1]=max(dp[i][j+1],dp[i][j]*2)

if dp[-1][-1]>10**18:
    print(-1)
else:
    print(dp[-1][-1])