感到了深深的绝望跪求为啥

#include<bits/stdc++.h>
using namespace std;
double h(double a,double b,double c,double d,double	s){
	s=sqrt((a-b)*(a-b)+(c-d)*(c-d));
	return s;
}
	
int main(){
		double s=0,s1,s2,s3,x1,x2,x3,y1,y2,y3;
	cin>>x1>>x2>>x3>>y1>>y2>>y3;
	s=(h(s1,x2,x1,y2,y1)+h(s2,x1,x3,y1,y3)+h(s3,x2,x3,y2,y3))%.2;
	cout<<s;
	return 0;
}

运行后还少1