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 <iomanip>
#include <cstdio>
#include <cmath>
using namespace std;

typedef struct vec vec;

struct vec {
    double x, y;
};


static double cross(vec a, vec b){  //外積
    return a.x * b.y - a.y * b.x;
}

int main(void){
    double x[21], y[21];
    int i, n = 0;
    double sum = 0;
    while(scanf("%lf,%lf", &x[n], &y[n]) != EOF)   n++;
    x[n] = x[0];
    y[n] = y[0];
    for(i = 0; i < n; i++){
        vec a = {x[i], y[i]};
        vec b = {x[i + 1], y[i + 1]};
        sum += cross(a,b);    
    }

    cout << fixed << setprecision(6) <<fabs(sum) / 2.0 << endl;
    return 0;
}