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:
#define	_USE_MATH_DEFINES
#include <iostream>
#include <iomanip>
#include <cctype>
#include <algorithm>
#include <functional>
#include <vector>
#include <cstdio>
#include <cstring>
#include <cmath>
#include <cfloat>
#include <map>
#include <queue>
#include <stack>
#include <list>
#include <string>
#include <set>
#include <complex>
#include <utility>
#include <numeric>
using namespace std;
typedef pair<double,double> P;


int main(){
	
	P p[50];
	char c;
	double ans=0;
	int n=1;
	while(cin>>p[n].first>>c>>p[n].second)
		n++;
	p[n+1].first=p[1].first;
	p[n+1].second=p[1].second;
	n--;
	for(int i=1;i<=n;i++){
		double s=0;
		s=(p[i].first-p[i+1].first)*(p[i].second+p[i+1].second);
		ans+=s;
	}
	
	printf("%.6f\n",abs(ans)/2);
	
	
	
}