#include<bits/stdc++.h> using namespace std;

int main(){ double x1,y1,x2,y2,x3,y3,p; double a,b,c,s; cin>>x1>>y1>>x2>>y2>>x3>>y3; a=sqrt((x2-x1)(x2-x1)+(y2-y1)(y2-y1)); b=sqrt((x2-x3)(x2-x3)+(y2-y3)(y2-y3)); c=sqrt((x3-x1)(x3-x1)+(y3-y1)(y3-y1)); p=(a+b+c)/2; s=sqrt(p*(p-a)(p-b)(p-c)); cout<<fixed<<setprecision(2)<<s; return 0; }

#include <bits/stdc++.h> 
using namespace std;

int main(){
double a,b,c,d,e,f,x,y,z,n,m; 
cin>>a>>b>>c>>d>>e>>f;
x=sqrt((a-c)*(a-c)+(b-d)*(b-d));
y=sqrt((a-e)*(a-e)+(b-f)*(b-f));
z=sqrt((e-c)*(e-c)+(f-d)*(f-d));
n=(x+y+z)/2;
m=sqrt(n*(n-x)*(n-y)*(n-z));
cout<<fixed<<setprecision(2)<<m;
return 0; }

#include <bits/stdc++.h> using namespace std;

int main(){ ** double a,b,c,d,e,f,x,y,z,n,m;** ** cin>>a>>b>>c>>d>>e>>f;** ** x=sqrt((a-c)*(a-c)+(b-d)*(b-d));** ** y=sqrt((a-e)*(a-e)+(b-f)*(b-f));** ** z=sqrt((e-c)*(e-c)+(f-d)*(f-d));** ** n=(x+y+z)/2;** ** m=sqrt(n*(n-x)*(n-y)*(n-z));** ** cout<<fixed<<setprecision(2)<<m;** ** return 0;** }