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<algorithm>
#include<vector>
#include<cstdio>
#include<cmath>
#define pb push_back
#define len(i,j) sqrt((a[i]-a[j])*(a[i]-a[j])+(b[i]-b[j])*(b[i]-b[j]))
using namespace std;
int main(){
vector<double>in,a,b;
double c,d,sum=0;
char x;
for(int i=0;i<2;i++){
cin>>c>>x>>d;
a.pb(c);
b.pb(d);
}
in.pb(len(1,0));
for(int i=2;scanf("%lf,%lf",&c,&d)!=EOF;i++){
double e;
a.pb(c);
b.pb(d);
in.pb(len(i,0));
e=len(i,i-1);
double z=(e+in[i-2]+in[i-1])/2;
sum+=sqrt(z*(z-e)*(z-in[i-2])*(z-in[i-1]));
}
cout<<sum<<endl;
}