AC 代码 | 答案

#include <bits/stdc++.h>
using namespace std;

double j(double a, double b, double c)
{
    double p = (a + b + c) / 2;
    double s = p * (p - a) * (p - b) * (p - c);
    return s;
}

int main()
{
    double a,b,c;
    cin >> a >> b >> c;
    printf("%.2lf", sqrt(j(a,b,c)));
    return 0;
}