#include <bits/stdc++.h>
const long long int INF = 2e9 + 999, MOD = 1e9 + 7, MAXN = 100001;
const long double EPS = 0.000001;
using namespace std;
bool sq(int x) {
  int a = (int)(sqrt(x) + EPS);
  if (a * a != x) {
    return 0;
  }
  return 1;
}
int main() {
  int n;
  cin >> n;
  vector<int> a(n);
  for (int i = 0; i < n; ++i) {
    cin >> a[i];
  }
  int ans = -INF;
  for (int i = 0; i < n; ++i) {
    if (!sq(a[i])) {
      ans = max(ans, a[i]);
    }
  }
  cout << ans;
  return 0;
}
