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))