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<cstdio>
#include<cmath>
using namespace std;
int main(){
long i,n;
char d;
double x[21],y[21],a,b,c,s;
for(i=0;i<20;i++){
cin>>x[i]>>d>>y[i];
if(cin.eof())break;
}
n=i;
for(s=0,i=0;i<n-1;i++){
a=sqrt((x[i]-x[0])*(x[i]-x[0])+(y[i]-y[0])*(y[i]-y[0]));
b=sqrt((x[i+1]-x[0])*(x[i+1]-x[0])+(y[i+1]-y[0])*(y[i+1]-y[0]));
c=sqrt((x[i+1]-x[i])*(x[i+1]-x[i])+(y[i+1]-y[i])*(y[i+1]-y[i]));
s+=sqrt((a+b+c)*(-a+b+c)*(a-b+c)*(a+b-c))*0.25;
}
printf("%.6f\n",s);
return 0;
}