# include<cstdio>
# include<iostream>
# include<cmath>
# include<cstring>
# include<algorithm>

using namespace std;

# define MAX 54*54

struct node
{
    int x,y;
}point[MAX];
int f[MAX];

void init()
{
    for ( int i = 0;i < MAX;i++ )
    {
        f[i] = i;
    }
}


struct edge
{
    int u,v;
    double cost;
}e[MAX];

int cmp( const struct edge & a,const struct edge & b )
{
    return a.cost < b.cost;
}

double dis ( node a,node b )
{
    return sqrt((a.x-b.x)*(a.x-b.x)+(a.y-b.y)*(a.y-b.y) );
}

int getf( int x )
{
    if ( f[x]==x )
        return x;
    else
    {
        int t = getf(f[x]);
        f[x] = t;
        return f[x];
    }
}

int main(void)
{
    int n;
    while ( scanf("%d",&n)!=EOF )
    {
        if ( n==0 )
            break;
        init();
        int p,q; scanf("%d%d",&p,&q);
        for ( int i = 1;i <= n;i++ )
        {
            scanf("%d%d",&point[i].x,&point[i].y);
        }
        int cnt = 0;
        for ( int i = 1;i <= n-1;i++ )
        {
            for ( int j = i+1;j <= n;j++ )
            {
                if( i==p&&j==q||i==q&&j==p )
                {
                    e[cnt].cost = 0;
                }
                else
                {
                    e[cnt].cost = dis(point[i],point[j]);
                }
                e[cnt].u = i; e[cnt].v = j;
                cnt++;
            }
        }
        int num = 0;
        double ans = 0;
        sort(e,e+cnt,cmp);
        ans = dis(point[p],point[q]);
        for ( int i = 0;i < cnt;i++ )
        {
            int x = getf(e[i].u);
            int y = getf(e[i].v);
            if ( x!=y )
            {
                num++;
                f[x] = y;
                ans+=e[i].cost;
                if(num==n-1)
                    break;
            }
        }
        printf("%.2lf\n",ans);
        memset(e,0,sizeof(e));
    }


    return 0;
}