N=int(input())
result=0
x,y,z=0,0,0
for i in range(N):
  a,b=map(int,input().split())
  if a%8==0:
    x+=b
  elif a%4==0:
    y+=b
  elif a%2==0:
    z+=b
result+=x
count=min(y,z)
result+=count
y-=count
z-=count
result+=y//2
if y%2==1:
  z+=1
result+=z//3

print(result)