题解 | #牛牛的圆#

知识点：运算

#include <iostream>
#include <cmath>
#include <iomanip>
using namespace std;

int main() {
    int r = 0;
    float pi = 3.14;
    float area = 0.0;

    cin >> r;

    area = pi * pow(r, 2);

    cout << fixed << setprecision(2);
    cout << area;

    return 0;
}