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 <stdio.h>
int main() {double coor[22][2],ans=0;int i=0,N;while (scanf("%lf,%lf",&coor[i][0],&coor[i][1])!=EOF) i++;for (N=0;N<i;N++) ans+=coor[N][0]*coor[(N+1)%i][1]-coor[N][1]*coor[(N+1)%i][0];if (ans<0) ans=-ans;printf("%.6lf\n",ans/2);return 0;}