delka = int(input())
	#pole = list(map(int, input().split(" ")))
	#print(delka, pole)
pole=[]
for x in range(0,delka,1):
	z = int(input())
	pole.append(z)
rozdil = pole[delka-1]-pole[delka-2]
#print(rozdil)
for n in range(delka-2,-1,-1):

	if pole[n]+rozdil!=pole[n+1]:
		print(str(n+2))
		quit()
print(str(1))