c语言距离函数，洛谷0分，求解疑

#include<stdio.h>
#include<math.h>
fun(double x1,double x2,double y1,double y2)
{
double dis;
dis=sqrt((x2-x1)(x2-x1)+(y2-y1)(y2-y1));
return dis;
}
int main()
{
int x1,y1,x2,y2,x3,y3;
double dis1,dis2,dis3,c;
scanf("%d%d%d%d%d%d",&x1,&y1,&x2,&y2,&x3,&y3);
dis1=fun(x1,x2,y1,y2);
dis2=fun(x1,x3,y1,y3);
dis3=fun(x3,x2,y3,y2);
c=dis1+dis2+dis3;
printf("%.2f",c);
return 0;
}