include

include

using namespace std; int main() {

int s = 1;
double n = 1.0, t = 1.0, pi = 0;
while (fabs(t) > 1e-4) {
	pi = pi + t;
	n = n + 2;
	s = -s;
	t = s / n;
}
pi = 4 * pi;
cout << pi;

}