public static void main(String[] args) {

int[] ns = {1, 4, 9, 16, 25};
for(int i=ns.length-1; i >-1; i--)
    System.out.println(ns[i]);

int sum = 0;

for(int n : ns) 

    sum += n;

System.out.println(sum);

double pi = 0;
for (int i=0; i< 1000000000; i++)
    pi += Math.pow(-1, i)*(4.0/(2*i+1));
System.out.println(pi);

}