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 double x[25],y[25],a,b,c,s,S = 0.0;
    int n = 0;
    while(scanf("%Lf,%Lf",&x[n],&y[n]) != EOF) n++;
    for(int i=1;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[i])*(x[i+1]-x[i])) + ((y[i+1]-y[i])*(y[i+1]-y[i])));
        c = sqrt(((x[0]-x[i+1])*(x[0]-x[i+1])) + ((y[0]-y[i+1])*(y[0]-y[i+1])));
        s = (a + b + c) / 2;
        S += sqrt(s*((s-a)*(s-b)*(s-c)));
    }
    printf("%Lf\n",S);
}