#!/usr/bin/python3

# 28-Z4-3: Množiny
# Autor: Martin Šerý

from bisect import bisect_left

#binary_search nam vrati index x v poli a[lo:hi] nebo -1 pokud se tam x nevyskytuje
def binary_search(a, x, lo=0, hi=None):
    hi = hi if hi is not None else len(a)
    pos = bisect_left(a,x,lo,hi)
    return (pos if pos != hi and a[pos] == x else -1)

N = int(input())
cisla = list(map(int, input().strip().split()))
cisla.sort()

for x in cisla:
    if (x == 1 and
        binary_search(cisla, x**2, x) != -1 and
        binary_search(cisla, x**3, x) != -1):
       print(x)
       break