80分求助

#include<bits/stdc++.h>
using namespace std;
int x_1,y_1,x_2,y_2,x_3,y_3,ans;
double a,b,c,s;
int main(){
	cin>>x_1>>y_1>>x_2>>y_2>>x_3>>y_3;
	a=sqrt((x_1-x_2)*(x_1-x_2)+(y_1-y_2)*(y_1-y_2));
	b=sqrt((x_2-x_3)*(x_2-x_3)+(y_2-y_3)*(y_2-y_3));
	c=sqrt((x_3-x_1)*(x_3-x_1)+(y_3-y_1)*(y_3-y_1));
	s=(a+b+c)/2;
	ans=ceil(sqrt(s*(s-a)*(s-b)*(s-c)));
	cout<<ans;
}