Problem: Write a program that reads the coordinates of the vertices of a convex n-sided polygon (a polygon whose internal angles are less than 180 degrees, that is, a polygon that is not dented) and outputs its area. The vertices are named Vertex 1, Vertex 2, Vertex 3, ... Vertex n according to the order of edge connections.

However, n is 3 or more and 20 or less. You can also use the following formula to find the area S from the lengths a, b, and c of the three sides of the triangle.

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input

The input is given in the following format:


x1, y1
x2, y2
::
xn, yn


xi and yi are real numbers that represent the x and y coordinates of vertex i, respectively.

output

Outputs the area S (real number) on one line. The output can contain an error of 0.000001 or less.

Example

Input

0.0,0.0
0.0,1.0
1.0,1.0
2.0,0.0
1.0,-1.0


Output

2.500000

Solution (in CPP):

Solution:
#include <stdio.h>
#include <math.h>
#include <complex>
#define rep(i, n) for (int i = 0; i < (int)(n); i++)
using namespace std;
typedef complex<double> P;

inline double cross(const P& a, const P& b) { return imag(conj(a)*b); }

int n;
P ps[32];

int main() {
    double x, y;
    while (scanf("%lf,%lf", &x, &y) != EOF) ps[n++] = P(x, y);
    double s = 0;
    rep (i, n-1) s += cross(ps[i]-ps[0], ps[i+1]-ps[0]);
    printf("%.9f\n", fabs(s)/2);
    return 0;
}