//tinh tich cac so chan tu so hoan chinh dau tien den so chinh phuong cuoi cung
//den so chinh phuong cuoi cung trong khoang tu 1 den n
#include <iostream>
using namespace std;
int cp(int n){
	for (int j = n; j >=9; j--) {
		int i = sqrt(j);
		if (i * i == j) {
			return j;
		}
	}
}
int chan(int n){
	if (n % 2 == 0) return 2;
	return 1;
}
int main(){
	int n, tich = 1;
	do {
		cout << "Nhap n: ";
		cin >> n;
	} while (n < 6);
	//So hoan chinh dau tien la 6
	for (int k = cp(n); k >= 6; k--){
		if (chan(k) == 2) tich = tich * k;
	}
	cout << "Dap an la: " << tich;
}