hdu4463

/*
分析：
    2012亚洲杭州站K题。
    水题。。。


                        2012-11-08
*/

#include"stdio.h"#include"string.h"#include"stdlib.h"#include"math.h"int pre[100];struct A{int a,b,len;}eage[3000];int k;int x[100],y[100];void build(int n){int i;for(i=0;i<n;i++)pre[i]=i;}int find(int k){if(pre[k]==k)return k;pre[k]=find(pre[k]);return pre[k];}void Union(int f1,int f2){pre[f1]=f2;}int cmp(const void *a,const void *b){struct A *c,*d;c=(struct A *)a;d=(struct A *)b;return c->len-d->len;}int main(){int n;int i,l;int d1,d2;int f1,f2;double ans;while(scanf("%d",&n),n){build(n);scanf("%d%d",&d1,&d2);d1--;d2--;for(i=0;i<n;i++)scanf("%d%d",&x[i],&y[i]);k=0;for(i=1;i<n;i++)for(l=0;l<i;l++){eage[k].a=i;eage[k].b=l;eage[k].len=(x[i]-x[l])*(x[i]-x[l])+(y[i]-y[l])*(y[i]-y[l]);k++;}qsort(eage,k,sizeof(eage[0]),cmp);ans=sqrt((double)(x[d1]-x[d2])*(x[d1]-x[d2])+(y[d1]-y[d2])*(y[d1]-y[d2]));Union(d1,d2);for(i=0;i<k;i++){f1=find(eage[i].a);f2=find(eage[i].b);if(f1==f2)continue;Union(f1,f2);ans+=sqrt((double)eage[i].len);}printf("%.2lf\n",ans);}return 0;}