#include "bits/stdc++.h"
using namespace std;
#define int long long
#define FOR(i, a, b) for(int i=(a);i<(b);i++)
#define RFOR(i, a, b) for(int i=(b-1);i>=(a);i--)
#define REP(i, n) for(int i=0; i<(n); i++)
#define RREP(i, n) for(int i=(n-1); i>=0; i--)
#define REP1(i, n) for(int i=1; i<=(n); i++)
#define RREP1(i, n) for(int i=(n); i>=1; i--)
#define ALL(a) (a).begin(),(a).end()
#define UNIQUE_SORT(l) sort(ALL(l)); l.erase(unique(ALL(l)), l.end());
#define CONTAIN(a, b) find(ALL(a), (b)) != (a).end()
#define out(...) printf(__VA_ARGS__)
#if DEBUG
#define debug(...) printf(__VA_ARGS__)
#else
#define debug(...) /* ... */
#endif

void solve();
signed main()
{
#if DEBUG
    std::ifstream in("input.txt");
    std::cin.rdbuf(in.rdbuf());
#endif
    cin.tie(0);
    ios::sync_with_stdio(false);
    solve();
    return 0;
}

/*================================*/
#if DEBUG
#define SIZE 100
#else
#define SIZE 223450
#endif

int N,M,X,Y;
struct Pos{double x,y;};
Pos P[SIZE];
double C[SIZE]; // コスト
set<int> E[SIZE];
struct Item{
    int i;
    double score;
    bool operator < (const Item& that) const {
        return score > that.score;
    }
};

double dist(int i, int j) {
    return sqrt(pow(P[i].x-P[j].x,2) + pow(P[i].y-P[j].y,2));
}

void solve() {
    cin>>N>>M>>X>>Y;
    X--;Y--;
    REP(i,N) {
        cin>>P[i].x>>P[i].y;
    }
    int u,v;
    REP(i,M) {
        cin>>u>>v;
        u--;v--;
        E[u].insert(v);
        E[v].insert(u);
    }
    REP(i,N)C[i]=LONG_LONG_MAX/3;
    priority_queue<Item> que;
    C[X]=0;
    que.push({X,0});
    while(que.size()) {
        auto item = que.top();
        int i = item.i;
        que.pop();
        if (item.score > C[i]) continue;
        for (int j:E[i]) {
            double n = C[i]+dist(i,j);
            if (C[j] > n) {
                C[j] = n;
                que.push({j,n});
            }
        }
    }
    out("%.10f\n",C[Y]);
}