n,p,k=map(int,input().split())
x=10**18
g=-1
items=[tuple(map(int,input().split())) for i in range(n)]
for i in range(k+1):
	f=p
	c=0
	d=0
	for j in range(n):
		t,b=items[j]
		if t==1:
			if c<i:
				f+=t
				c+=1
		else:
			if c+d<k and f<=x:
				f*=2
				d+=1
	if c+d==k and f<=x:
		g=max(g,f)
print(g)