filename = "example_B.txt"


def RecursivePart(Lines, Sum, row, column, number):
    Sum += number
    if len(Lines) == row+1:
        return Sum
    numbers = Lines[row+1].split()
    num_1 = int(numbers[column])
    num_2 = int(numbers[column+1])

    Sum_1 = 0
    Sum_2 = 0

    if not isPrime(num_1):
        Sum_1 = RecursivePart(Lines, Sum, row+1, column, num_1)

    if not isPrime(num_2):
        Sum_2 = RecursivePart(Lines, Sum, row+1, column+1, num_2)

    if Sum_1 > Sum_2:
        return Sum_1
    return Sum_2



def isPrime(number):
    if number == 1 or number == 0:
        return False
    for i in range(2,number):
        if number % i == 0:
            return False
    return True


def Algorithm(input):
    file1 = open(input, 'r')
    Lines = file1.readlines()

    result = 0

    first_num = int(Lines[0].split()[0])

    if not isPrime(first_num):
        result = RecursivePart(Lines, 0, 0, 0, first_num)

    print(result)



if __name__ == '__main__':
    Algorithm(filename)