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.

<image>



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 <bits/stdc++.h>
#define REP(i,n) for(int i=0; i<(int)(n); ++i)

using namespace std;


typedef complex<double> Point;
const double EPS = 1e-8;
typedef vector<Point> Polygon;
Point curr(const Polygon& a, int x){ return a[x]; }
Point next(const Polygon& a, int x){ return a[(x + 1) % a.size()]; }
double cross(Point a, Point b){
    return imag(conj(a) * b);
}
double area(const Polygon& P) {
    double A = 0;
    for(int i = 0; i < P.size(); i++){
        A += cross(curr(P, i), next(P, i));
    }
    return abs(A) / 2.0;
}


int main(){
    double x, y;
    Polygon P;
    while(scanf("%lf,%lf", &x, &y) != EOF){
        P.push_back(Point(x, y));
    }
    printf("%.12f\n", area(P));
    return 0;
}