B2606为啥WA？

#include <bits/stdc++.h>

using namespace std;

const double PI = 3.141593;

int main() {
    double r = 5;
    double C = 2 * r * PI;
    double S = PI * pow(r, 2);
    double V = (4 / 3) * PI * pow(r, 3);
    cout << C << endl;
    cout << S << endl;
    cout << V << endl;

    return 0;
}