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<cstdio>
#include<algorithm>
#include<vector>
#include<string>
#include<iostream>
#include<queue>
#include<map>
#include<set>
#include<complex>
#include<stack>
#include<cmath>
 
using namespace std;
 
#define reps(i,f,n) for(int i=f;i<int(n);i++)
#define rep(i,n) reps(i,0,n)

#define X real()
#define Y imag()
typedef complex<double> P;

double cross(P a,P b){return a.X*b.Y-a.Y*b.X;}
int main(){
	
	double a,b;
	vector<P> p;
	while(scanf("%lf,%lf",&a,&b)!=EOF){
		p.push_back(P(a,b));
	}
	
	double sum = 0;
	reps(i,1,p.size()-1){
		sum += cross(p[i]-p[0],p[i+1]-p[0])/2;
	}
	
	printf("%.9lf\n",fabs(sum));
	
}