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