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

#define DIM	2		/* Dimension of points */
typedef int     tPointi[DIM];   /* type integer point */

#define PMAX	1000		/* Max # of pts in polygon */
typedef tPointi tPolygoni[PMAX];/* type integer polygon */
 
int     Area2( tPointi a, tPointi b, tPointi c );
int     AreaPoly2( int n, tPolygoni P );


main()
{
	int	n,a=0;
	tPolygoni	P;

	n = ReadPoints( P );
	a =abs( AreaPoly2(n,P)/2);	
 	printf("%d",a);	
	return a;
}

/* 
        Returns twice the signed area of the triangle determined by a,b,c,
        positive if a,b,c are oriented ccw, and negative if cw.
*/
int     Area2( tPointi a, tPointi b, tPointi c )
{
/*	The text has this:
        return
                a[0] * b[1] - a[1] * b[0] +
                a[1] * c[0] - a[0] * c[1] +
                b[0] * c[1] - c[0] * b[1];

	The following computation is algebraically equivalent but
	uses four fewer multiplications.  It is obtained by shifting the
	coordinate system so that point a is the origin.
*/

	return
		(b[0] - a[0]) * (c[1] - a[1]) -
		(c[0] - a[0]) * (b[1] - a[1]);
}

/*      
        Returns twice the area of polygon P.
*/
int     AreaPoly2( int n, tPolygoni P )
{
        int     i;
        int     sum = 0;        /* Partial area sum */

        for (i = 1; i < n-1; i++)
                sum += Area2( P[0], P[i], P[i+1] );
        return  sum;
}

int	ReadPoints( tPolygoni P)
/*
        Reads in the coordinates of the vertices of a polygon from stdin,
        puts them into P, and returns n, the number of vertices.
        The input is assumed to be pairs of whitespace-separated coordinates,
        one pair per line.  The number of points is not part of the input.
*/
{
        int     n = 0;
	char *s1 =(char *) malloc(sizeof(char)*10),*s2 =(char *) malloc(sizeof(char)*10);
	
/*	printf("Polygon:\n");
        printf("  i   x   y\n"); */
        while ( (n < PMAX) &&
                (scanf("%s %s",s1,s2) /* &P[n][0],&P[n][1]) */  != EOF) ) {
		if (n==0) sscanf(s1,"[[%d",&P[n][0]); else sscanf(s1,"[%d",&P[n][0]);
		sscanf(s2,"%d",&P[n][1]);
/*                printf("%3d%4d%4d\n", n, P[n][0], P[n][1]);  */
                ++n;
        }
        if (n < PMAX)
/*                printf("n = %3d vertices read\n",n); */;
        else    /* printf("Error in ReadPoints:\ 
                        too many points; max is %d\n", PMAX); */;
/*        putchar('\n'); */
 
        return  n;
}