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<iostream>
#include<algorithm>
#include<cmath>
#include<cstdio>
#include<vector>
using namespace std;

int main(){
    vector<double> x, y;
    double a, b, c, s;
    while(~scanf("%lf,%lf", &a, &b)){
	x.push_back(a);
	y.push_back(b);
    }
    for(int i = 1;i <= x.size();i++){
	x[i%x.size()] -= x[0];
	y[i%x.size()] -= y[0];
    }
    double res = 0;
    for(int i = 1;i < x.size() - 1;i++){
	res += fabs(x[i] * y[i + 1] - y[i] * x[i + 1]);
    }
    printf("%.9lf\n", res / 2);
    return 0;
}