include <bits/stdc++.h>

using namespace std;

int main() {

int n;
cin >> n;
int c = -1100000;
for (int i = 1; i <= n; i++) {
	int m;
	cin >> m;
	double d = sqrt (m);
	int a = int (d);
	if (a == d) {
		if (c > m) {
			c = max(c, m);
		}
	}
}
cout << c;
return 0;

}