蒟蒻求助

#include<bits/stdc++.h>
using namespace std;
 double a[3],b[3],j[3];
 double k=0;
double g(long double f,long double r,long double q,long double x)
{
    return sqrt((r-f)*(r-f)+(x-q)*(x-q));
}

int main(){
    for(int i=0;i<3;i++)
        cin>>a[i]>>b[i];
    j[0]=g(a[0],a[1],b[0],b[1]);
    j[1]=g(a[1],a[2],b[1],b[2]);
    j[2]=g(a[2],a[3],b[2],b[3]);
    k=k+j[0]+j[1]+j[2];
    printf("%.2f",k);
}

20分，后面4个点WA