#include <cstdio>
#include <iostream>
#include <cmath>

using namespace std;

struct punct
{
    double x,y;
};

double pdist(punct a,punct b)
{
    return ((a.x-b.x)*(a.x-b.x)+(a.y-b.y)*(a.y-b.y));
}

double aria(punct a,punct b,punct c)
{
    return (sqrt(pdist(a,b)*pdist(a,c))/2);
}

int main()
{
    punct a,b,c;
    cin>>a.x>>a.y;
    cin>>b.x>>b.y;
    cin>>c.x>>c.y;

    printf("%.7lf", aria(a,b,c));
    return 0;
}