#include <iostream>
#include <cmath>

using namespace std;

struct Point
{
    float x;
    float y;
};

float dlugosc(Point a, Point b)
{
    float dlugosc;
    dlugosc=sqrt(((a.x-b.x)*(a.x-b.x))+((a.y-b.y)*(a.y-b.y)));
    return dlugosc;
}

float poletrojkata(Point a, Point b, Point c)
{
    float A = dlugosc(b, c);
    float B = dlugosc(a, c);
    float C = dlugosc(a, b);

    float p;
    p=(A + B + C)/2;
    return sqrt(p*(p-A)*(p-B)*(p-C));
}

int main()
{
    Point a, b, c;
    a.x = 0;
    a.y = 0;
    b.x = 4;
    b.y = 0;
    c.x = 0;
    c.y = 3;
    cout << poletrojkata(a, b, c);
    return 0;
}