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

# 8
v = count[0]
ans += v
count[0] -= v

# 42
v = min(count[1],count[2])
ans += v
count[1] -= v
count[2] -= v

# 44
v = count[1]//2
ans += v
count[1] -= v*2

# 222
v =count[2]//3
ans += v
count[2] -= v*3

print(ans)