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 <string>
#include <vector>
#include <cmath>
#include <algorithm>
#include <cstdlib>
#include <ctime>
#include <cstdio>
#include <functional>
#include <set>
#include <queue>
#include <cctype>
#include <climits>
#include <stack>
using namespace std;
   
  
   
int main(){
   

	vector<double> xs,ys;
	double x,y;	
	while(scanf("%lf,%lf",&x,&y)!=EOF){
		 xs.push_back(x);
		 ys.push_back(y);
	}

	xs.push_back(xs[0]);
	ys.push_back(ys[0]);

	double res=0;
	for(int i=0;i<xs.size()-1;i++){
		res+=(xs[i]-xs[i+1])*(ys[i]+ys[i+1]);
	} 

	printf("%.10f\n",abs(res/2.0));

}