s = 0
min_delta = 10001
n = int(input())
for i in range(n):
    a, b = map(int, input().split())
    if a < b:
        a, b = b, a

    s += a
    delta = a - b
    if delta % 3 != 0 and delta < min_delta:
        min_delta = delta

if s % 3 != 0:
    print(s)
elif min_delta % 3 != 0 and min_delta < 10001:
    print(s - min_delta)
else:
    print(0)