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

最后一个点过不了啊，大佬们多多指教