错的是最后一组样本点，我给下载下来了，自测是和给的输出一样的

#include <iostream>
#include <cmath>
#include <iomanip>
#include <vector>
#include <algorithm>
#include <cstdlib>
#include <string>
#define un unsigned
typedef long long ll;
double my(double a, double b, double c, double d)
{
	return pow((pow(abs(a - c), 2) + pow(abs(b - d), 2)), 0.5);
}
using namespace std;
int main()
{
	ios_base::sync_with_stdio(false);
	cin.tie(0);
	cout.tie(0);
	double a[6];
	for (int i = 0; i < 6; i++)
		cin >> a[i];
	double sum = 0;
	sum += my(a[0], a[1], a[2], a[3]);
	sum += my(a[0], a[1], a[4], a[5]);
	sum += my(a[4], a[5], a[2], a[3]);
	cout << fixed << setprecision(2) << sum;
	return 0;
}