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 <cstdio>
#include <iostream>
#include <algorithm>
#include <cstdlib>
#include <cmath>
#include <vector>
#include <ctime>
#include <string>
#include <map>
#include <stack>
#include <queue>
#include <complex>

using namespace std;

typedef complex<double> xy_t;
char c;
double x, y;
xy_t P[20];
const int MAX = 10000000;

double cross_product(xy_t a, xy_t b) { return (conj(a)*b).imag(); }

int main(void){

	
	int k = 0;
	while(cin >> x >> c >> y){
		P[k] = xy_t(x, y);
		k++;
	}

	
	double ans = 0;

	for(int i = 1; i < k - 1; i++){
			ans += abs(0.5 * cross_product(xy_t (P[i] - P[0]), xy_t (P[i + 1] - P[0])));
	}


	printf("%.6f\n", ans);
	
    return 0;
}