(n,),*e=[[*map(int,s.split())]for s in open(0)]
d=[0]*4
for a,b in e:
  t=0
  while a%2==0 and t<3:
    t+=1
    a//=2
  d[t]+=b
ans=d[3]
m=min(d[1],d[2])
d[2]-=m
d[1]-=m
ans+=m+d[2]//2+d[1]//3
print(ans)