import sys
input = sys.stdin.readline

N=int(input())

A=[0,0,0]

for i in range(N):
    a,b=map(int,input().split())

    count=0
    while a%2==0:
        count+=1
        a//=2

    if count==1:
        A[0]+=b
    elif count==2:
        A[1]+=b
    elif count>=3:
        A[2]+=b

#print(A)

ANS=A[2]

MIN=min(A[0],A[1])

ANS+=MIN
A[0]-=MIN
A[1]-=MIN

ANS+=A[0]//3+A[1]//2

print(ANS)