n=int(input())

c=[0,0,0]

for _ in range(n):
  a,b=map(int,input().split())
  if a%8==0:
    c[2]+=b
  elif a%4==0:
    c[1]+=b
  elif a%2==0:
    c[0]+=b
    
ans=min(c[0],c[1])
c[0]-=ans
c[1]-=ans

print(ans+c[2]+c[0]//3+c[1]//2)