#include <bits/stdc++.h>
using namespace std;
typedef signed long long ll;

#undef _P
#define _P(...) (void)printf(__VA_ARGS__)
#define FOR(x,to) for(x=0;x<(to);x++)
#define FORR(x,arr) for(auto& x:arr)
#define ITR(x,c) for(__typeof(c.begin()) x=c.begin();x!=c.end();x++)
#define ALL(a) (a.begin()),(a.end())
#define ZERO(a) memset(a,0,sizeof(a))
#define MINUS(a) memset(a,0xff,sizeof(a))
//-------------------------------------------------------

int N,M;
int S,T;
int X[202020],Y[202020];
vector<int> E[202020];
double D[202020];

void solve() {
	int i,j,k,l,r,x,y; string s;
	
	cin>>N>>M>>S>>T;
	S--,T--;
	FOR(i,N) cin>>X[i]>>Y[i];
	FOR(i,M) {
		cin>>x>>y;
		E[x-1].push_back(y-1);
		E[y-1].push_back(x-1);
	}
	
	FOR(i,N) D[i]=1e9;
	D[S]=0;
	priority_queue<pair<double,int>> Q;
	Q.push({0,S});
	while(Q.size()) {
		double co=-Q.top().first;
		int cur=Q.top().second;
		Q.pop();
		if(D[cur]!=co) continue;
		FORR(e,E[cur]) {
			double d=co+hypot(X[cur]-X[e],Y[cur]-Y[e]);
			if(D[e]>d) {
				D[e]=d;
				Q.push({-d,e});
			}
		}
		
	}
	_P("%.12lf\n",D[T]);
}


int main(int argc,char** argv){
	string s;int i;
	if(argc==1) ios::sync_with_stdio(false), cin.tie(0);
	FOR(i,argc-1) s+=argv[i+1],s+='\n'; FOR(i,s.size()) ungetc(s[s.size()-1-i],stdin);
	cout.tie(0); solve(); return 0;
}