def main():
    n = int(input())
    a = [1]
    for i in range(n):
        add = int(input()) - a[i] if i%2 == 0 else a[i] - int(input())
        if add >= 1:
            a.append(add)
        else:
            break
    if len(a) != n+1:
        print(-1)
    else:
        print(n+1)
        [print(i) for i in a]


if __name__ == "__main__":
    import sys
    import os
    if len(sys.argv) > 1:
        if sys.argv[1] == "-d":
            filename = "input1.txt"
            fd = os.open(filename, os.O_RDONLY)
            os.dup2(fd, sys.stdin.fileno())
            main()
    else:
        main()