#include <stdio.h>
#include <stdlib.h>
#include <math.h>

int main ()
{
   float x1, y1, x2, y2, x3, y3;
   float a, b, c;
   float s;
   float A;

   /* Read the coordinates of the three vertices */
   printf("(x1,y1) = "); scanf("%f%f", &x1, &y1);
   printf("(x2,y2) = "); scanf("%f%f", &x2, &y2);
   printf("(x3,y3) = "); scanf("%f%f", &x3, &y3);

   /* Compute the lengths of the sides */
   a = sqrt((x2-x3)*(x2-x3)+(y2-y3)*(y2-y3));
   b = sqrt((x3-x1)*(x3-x1)+(y3-y1)*(y3-y1));
   c = sqrt((x1-x2)*(x1-x2)+(y1-y2)*(y1-y2));

   /* Compute the semiperimeter */
   s = (a + b + c) / 2;

   /* Compute the area */
   A = sqrt(s*(s-a)*(s-b)*(s-c));

   /* Report the area */
   printf("Area = %f\n", A);

   exit(0);
}