#include<bits/stdc++.h>
using namespace std;
int main() {
    int x1,y1,x2,y2,c1,c2,a,b,c;
    cin>>x1>>y1>>x2>>y2>>c1>>c2;
    a=sqrt((x1-x2)*(x1-x2)+(y1-y2)*(y1-y2));
    b=sqrt((x1-c1)*(x1-c1)+(y1-c2)*(y1-c2));
    c=sqrt((x2-c1)*(x2-c1)+(y2-c2)*(y2-c2));
    double s=0.5*(a+b+c);
    cout<<fixed<<setprecision(0)<<sqrt(s*(s-a)*(s-b)*(s-c));
    return 0; 
}

各路大神求解