try:	
	delka = int(input())
	pole = list(map(int, input().split(" ")))

	#print(delka, pole)
	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))
except:
	raise EOFError