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 <algorithm>
#include <string>
#include <stack>
#include <cstdlib>
#include <queue>
#include <vector>
#include <set>
#include <stdio.h>
#include <cstdio>
#include <cmath>
#include <complex> 
using namespace std;
typedef complex<double> xy_t;
xy_t P[30];
int N=0;
double x,y;
int main() {
double s =0.0;
while (scanf("%lf,%lf", &x,&y) != EOF) {
	P[N] = xy_t(x,y);
	N += 1;
}
for ( int i = 0; i+2 < N;i++ ){
	xy_t a = P[i+1] - P[0], b = P[i+2]-P[0];
	s += - (a.real()*b.imag()-a.imag()*b.real())/2;
}
printf("%.6f\n", abs(s));
}