вот подобное задание было

path = '27-1b.txt'
task_file = open(path)

n = int(task_file.readline())

res = 0
min_razn_1 = 1000000
min_razn_2 = 1000000
for i in range(n):
    x,y = map(int,task_file.readline().split())
    res += max(x,y)
    if abs(x-y) % 3 == 1:
        min_razn_1 = min(min_razn_1,abs(x-y))
    elif abs(x-y) % 3 == 2:
        min_razn_2 = min(min_razn_2,abs(x-y))

if res % 3 != 0:
    if res % 3 == 1:
      res -= min_razn_1
    elif res % 3 == 2:
      res -= min_razn_2
print(res)