try:
    while 1:
        N = int(input())
        if N <= 2:
            print (1)
            continue
        l = list(map(int, input().split()))[::-1]
        last = l[1]
        diff = l[0]-l[1]
        for i, n in enumerate(l[2:]):
            if last-n != diff:
                print(N-i-1)
                break
            last = n
        else:
            print(1)
except EOFError:
    pass