#include <cstdio>
#include <cmath>
#include <cstring>
#include <algorithm>
#include <queue>
using namespace std;
struct edge
{
    int f,t;
    double l;
} e[2501];
bool operator<(const edge&lhs,const edge&rhs)
{
    return lhs.l>rhs.l;
}
int X[53],Y[53];
int f[53];
int fa(int x){return f[x]==x?x:f[x]=fa(f[x]);}
int main()
{
    int n,p,q;
    while(scanf("%d",&n),n)
    {
        priority_queue<edge> Q;
        for(int i=0;i<53;i++) f[i]=i;
        scanf("%d%d",&p,&q),p--,q--;
        for(int i=0; i<n; i++)
            scanf("%d%d",X+i,Y+i);
        for(int i=0; i<n; i++)
            for(int j=0; j<n; j++)
                e[i*n+j]= {i,j,sqrt((X[i]-X[j])*(X[i]-X[j])+(Y[i]-Y[j])*(Y[i]-Y[j]))};
        double ans=e[p*n+q].l;
        f[fa(p)]=fa(q);
        for(int i=0; i<n; i++)
            for(int j=0; j<n; j++)
                Q.push(e[i*n+j]);
        int cnt=n-1;
        while (!Q.empty())
        {
            edge e = Q.top();
            Q.pop();
            if (fa(e.f) != fa(e.t))
            {
                f[fa(e.f)] = fa(e.t);
                ans += e.l;
                cnt--;
                if (cnt == 1) break;
            }
        }
        printf("%.2lf\n", ans);
    }
    return 0;
}