/* -*- coding: utf-8 -*-
 *
 * 1065.cc:  No.1065 電柱 / Pole (Easy) - yukicoder
 */

#include<cstdio>
#include<cstdlib>
#include<cstring>
#include<cmath>
#include<iostream>
#include<string>
#include<vector>
#include<map>
#include<set>
#include<stack>
#include<list>
#include<queue>
#include<deque>
#include<algorithm>
#include<numeric>
#include<utility>
#include<complex>
#include<functional>
 
using namespace std;

/* constant */

const int MAX_N = 200000;
const double DINF = 1e62;

/* typedef */

typedef pair<double,int> pdi;
typedef vector<pdi> vpdi;

/* global variables */

int xs[MAX_N], ys[MAX_N];
vpdi nbrs[MAX_N];
double ds[MAX_N];

/* subroutines */

inline double dist(int i, int j) {
  int dx = xs[j] - xs[i], dy = ys[j] - ys[i];
  return sqrt(dx * dx + dy * dy);
}

/* main */

int main() {
  int n, m, st, gl;
  scanf("%d%d%d%d", &n, &m, &st, &gl);
  st--, gl--;

  for (int i = 0; i < n; i++) scanf("%d%d", xs + i, ys + i);

  for (int i = 0; i < m; i++) {
    int u, v;
    scanf("%d%d", &u, &v);
    u--, v--;
    double d = dist(u, v);
    nbrs[u].push_back(pdi(d, v));
    nbrs[v].push_back(pdi(d, u));
  }

  fill(ds, ds + n, DINF);
  ds[st] = 0.0;

  priority_queue<pdi> q;
  q.push(pdi(0.0, st));

  while (! q.empty()) {
    pdi u = q.top(); q.pop();
    double ud = -u.first;
    int ui = u.second;
    if (ud != ds[ui]) continue;
    if (ui == gl) break;

    vpdi &nbru = nbrs[ui];
    for (vpdi::iterator vit = nbru.begin(); vit != nbru.end(); vit++) {
      int vi = vit->second;
      double vd = ud + vit->first;
      if (ds[vi] > vd) {
	ds[vi] = vd;
	q.push(pdi(-vd, vi));
      }
    }
  }

  printf("%.6lf\n", ds[gl]);
  return 0;
}