#include <iostream>
#include <vector>
#include <set>
#include <bitset>
#include <algorithm>

using namespace std;

int main() {
set<long long> sq;
for (long long i =0; i*i <= 1e6 + 1 ; ++i) {
sq.insert(i*i);
}
long long n;
cin » n;
long long ans = -1;
for (long long i = 0; i < n; ++i) {
long long a;
cin » a;
if (sq.find(a) == sq.end() && a > ans) {
ans = a;
}
}
cout « ans;
return 0;
}