#inclue <bits/stdc++.h>
using namespace std;
double a;
int main()
{
cin>>a;
if (a<=0) cout<<"khong phai";
else cout<<fixed<<setprecision(2)<<a*a;
return 0;
}
code bằng python
a = input('nhap a ')
if a>0:
print('a la canh cua hinh vuong. Dien tich S = ', a**2)
else:
print('a khong phai la canh hinh vuong')