#include <iostream>
#include<cstdio>
#include<cstring>
#include<climits>
#include<cmath>
using namespace std;

double sum;
int i,j,n;
bool vis[55];
int x[55],y[55];
double dis[55],mp[55][55];
void prim()
{
    for(int i=1;i<n-1;i++)
    {
        double minn=INT_MAX*1.0;
        int k;
        for(int j=1;j<=n;j++)
          if (!vis[j] && dis[j]<minn)
          {
              k=j;
              minn=dis[j];
          }
        vis[k]=1;
        sum+=minn;
        for(int j=1;j<=n;j++)
        if (!vis[j] && mp[k][j]<dis[j]) dis[j]=mp[k][j];
    }
    return;
}
int main()
{
    while(scanf("%d",&n) && n)
    {
        int u,v;
        memset(vis,0,sizeof(vis));
        scanf("%d%d",&u,&v);
        for(i=1;i<=n;i++)
            scanf("%d%d",&x[i],&y[i]);
        for(i=1;i<=n;i++)
            for(j=i+1;j<=n;j++)
        {
            double d=sqrt(pow(x[i]-x[j],2)+pow(y[i]-y[j],2));
            mp[i][j]=d;
            mp[j][i]=d;
        }
       sum=mp[u][v];//先把那两家店连起来
       vis[u]=1;
       vis[v]=1; //全部标记走过
       for(i=1;i<=n;i++)  dis[i]=mp[u][i];
       for(i=1;i<=n;i++)  dis[i]=min(dis[i],mp[v][i]);//预处理到其他点的距离
       prim();
       printf("%.2lf\n",sum);
    }
    return 0;
}