#include<iostream>
#include<iomanip>
#include<cmath>
#include <algorithm>
using namespace std;
int n;
struct point{
	int x,y,z;
}a[100010];
bool cmp(point a,point b){
	return a.z<b.z;
}
double ans=0.00;
int main(){
	cin>>n;
	for(int i=1;i<=n;i++){
		cin>>a[i].x>>a[i].y>>a[i].z;
	}
	sort(a+1,a+1+n,cmp);
	for(int i=1;i<=n;i++){
		ans+=(sqrt(1.00*(a[i].x-a[i+1].x)*(a[i].x-a[i+1].x)+(a[i].y-a[i+1].y)*(a[i].y-a[i+1].y)+(a[i].z-a[i+1].z)*(a[i].z-a[i+1].z)));
	}
	cout<<fixed<<setprecision(3)<<ans;
	return 0;
}

为什么我的答案比正确答案多好多？ 大佬救命