try:	
	delka = input()
	while delka!="":
		delka=int(delka)
		pole = list(map(int, input().split(" ")))
		#print(delka, pole)
		j=0
		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))
					j=j+1
					break		
		if j==0	:
			print(str(1))
		delka=input()
except:
	EOFError
#print(vysledek)

#delka = input()