代码如下：

#include<bits/stdc++.h>
using namespace std;
double dis(double x1,double y1,double x2,double y2){
	return sqrt(pow((x1-x2),2)+pow((y1-y2),2));
}
int main(){
	int x1,y1,x2,y2,x3,y3;
	cin>>x1>>y1>>x2>>y2>>x3>>y3;
	double d1=dis(x1,y1,x2,y2);
	double d2=dis(x2,y2,x3,y3);
	double d3=dis(x1,y1,x3,y3);
	double c=d1+d2+d3;
	cout << fixed << setprecision(2) << c;
	return 0;
}