N = int(input())
maxszel = 0
T = []
for i in range(N):
    T.append(int(input()))
tores = False
for i in range(1,N):
    if T[i] > T[i-1]:
        tores = True
        break
if not tores:
    print(-1)
else:
    maxszel = -1
    i = 0
    while i < N-2 and i + maxszel < N:
        if T[i] > T[i+1]:
            maxv = T[i]
            j = i + 1
            while j < N-1 and T[j] < maxv:
                j += 1
                if T[j] > maxv:
                    if j - i > maxszel:
                        maxszel = j - i
                    maxv = T[j]
            if T[j] >= maxv:
                i = j
            else:
                i += 1
        else:
            i += 1
    print(maxszel)