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 <cmath>
const int MAX = 21;
typedef double D;
 
D dis(D x1,D y1,D x2,D y2){
  D d;
  d = sqrt(pow(x2-x1,2)+pow(y2-y1,2));
  return d;
}
 
int main(){
  D x[MAX],y[MAX];
  int t = 0;
  D S = 0.0,z,a,b,c;
 
  while(true){
    if(scanf("%lf,%lf",&x[t] ,&y[t]) == EOF) break;
    t++;
  }
 
  for(int i = 2 ; i < t ; i++){
    a = dis(x[0],y[0],x[i-1],y[i-1]);
    b = dis(x[0],y[0],x[i],y[i]);
    c = dis(x[i-1],y[i-1],x[i],y[i]);
    z = (a + b + c) / 2;
 
    S += sqrt(z*(z-a)*(z-b)*(z-c));
  }
  
  printf("%.6f\n",S);
 
  return 0;
}