#include <cstdio>
#include <iostream>
#include <fstream>
#include <vector>
#include <list>
#include <map>
#include <set>
#include <queue>
#include <stack>
#include <bitset>
#include <algorithm>
#include <sstream>
#include <iomanip>
#include <cmath>
#include <cstdlib>
#include <cctype>
#include <cstring>
#include <string>
#include <ctime>
#include <cassert>
#include <utility>

using namespace std;

double ax, ay, bx, by, cx, cy;
double a, b, c;

double dist(double ax, double ay, double bx, double by) {
    double dx = ax - bx;
    double dy = ay - by;
    return sqrt(dx * dx + dy * dy);
}

double calcArea(double ax, double ay, double bx, double by, double cx, double cy) {
    double ret = (bx - ax) * (cy - ay) - (by - ay) * (cx - ax);
    ret = fabs(ret) / 2.0;
    return ret;
}

int main() {
//	freopen("date.in", "r", stdin);
//	freopen("date.out","w", stdout);
	
	cin >> ax >> ay >> bx >> by >> cx >> cy;
	
	double ans = calcArea(ax, ay, bx, by, cx, cy);
	
	printf("%.6lf\n", ans);
	
	return 0;
}