double pi = 0;

double tmp = 0;

for (long i = 1; i < 1000000000; i += 2) {

// TODO:

if((i - 1) / 2 % 2 == 0) {

tmp =  tmp + ( 1.0 / i );

}

else {

tmp =  tmp - ( 1.0 / i );

}

}

pi = tmp * 4;

System.out.println(pi);