#include <iostream>
#include <vector>
#include <climits>
#include <algorithm>
#include <cmath>
#include <map>
#include <set>
#include <string>
#include <bitset>
#include <utility>
#include <numeric>
#include <queue>
#include <stack>

using ll = long long;
using namespace std;

constexpr int MOD = 1e9 + 7;
constexpr ll MOD_LL = ll(1e9) + 7;

int main(void) {
	int n, m, x, y;
	cin >> n >> m >> x >> y;
	
	x--; y--;
	vector<int> p(n), q(n);
	for(int i = 0; i < n; ++i) {
		cin >> p[i] >> q[i];
	}
	
	vector< vector<int> > G(n);
	for(int i = 0; i < m; ++i) {
		int a, b;
		cin >> a >> b;
		a--; b--;
		
		G[a].push_back(b);
		G[b].push_back(a);
	}
	
	vector<double> dist(n, 1e9 + 10);
	dist[x] = 0.0;
	
	priority_queue< pair<double, int> > que;
	que.push( {0.0, x} );
	
	while( !que.empty() ) {
		double now_cost = -que.top().first;
		int now = que.top().second;
		que.pop();
		
		if( dist[now] != now_cost ) continue;
		
		for(auto &to : G[now]) {
			double cost = now_cost + sqrt((p[now] - p[to]) * (p[now] - p[to]) + (q[now] - q[to]) * (q[now] - q[to]));
			
			if( dist[to] > cost ) {
				dist[to] = cost;
				que.push( {-cost, to} );
			}
		}
	}

	printf("%.12f\n", dist[y]);
	
	return 0;
}