from sys import stdin

def main():
    N = int(input())
    L = stdin.read().splitlines()

    num = [sum(a * 4 if i % 2 else a for i, a in enumerate(map(int, j.split()))) for j in L]
    judge = not len({map(lambda x: x % 2, num)}) - 1
    if judge:
        print((max(num) * N - sum(num)) // 2)
    else:
        print(-1)

main()