n, m = map(int, input().split())
if n % 2 == 1 or m % 2 == 1:
    print(-1)
    exit()
print(n*m - 1)
for i in range(0, n, 2):
    for j in range(0, n, 2):
        if i % 4 == 0:
            if j == 0:
                print(i+1, j+2)
                print(i+2, j+1)
            else:
                print(i+2, j+1)
                print(i+1, j+2)
            print(i+1, j+1)
            print(i+2, j+2)
        else:
            print(i+1, j+2)
            print(i+2, j+1)
            if j == 0:
                print(i+2, j+2)
                print(i+1, j+1)
            else:
                print(i+1, j+1)
                print(i+2, j+2)