#include <cstdio>
#include <cstring>
#include <cmath>
#include <algorithm>
#include <vector>
#include <queue>

int main()
{
    /* input */
    int N, M;
    int X, Y;
    int p[200000], q[200000];
    int maxp = 0, maxq = 0;
    int P[200000], Q[100000];
    scanf( " %d %d", &N, &M );
    scanf( " %d %d", &X, &Y );
    std::vector<std::vector<int>> list_lines(N);
    for ( int i=0; i<N; i++ ) {
        scanf( " %d %d", p+i, q+i );
        if ( maxp < std::abs(p[i]) ) maxp = std::abs(p[i]);
        if ( maxq < std::abs(q[i]) ) maxq = std::abs(q[i]);
    }
    for ( int i=0; i<M; i++ ) {
        scanf( " %d %d", P+i, Q+i );
        list_lines[P[i]-1].push_back(Q[i]);
        list_lines[Q[i]-1].push_back(P[i]);
    }
    for ( int i=0; i<N; i++ ) {
        for ( int j=1; j<N; j++ ) {
            if( p[i] == p[j] and q[i] == q[j] ) {
                list_lines[i].push_back(j+1);
                list_lines[j].push_back(i+1);
            }
        }
    }

    /* process */
    double cost[200000];
    double maxcost = ( maxp + maxq ) * 2.0;
    for ( int i=0; i<N; i++ ) {
        cost[i] = maxcost;
    }
    std::queue<int> q_graph;
    q_graph.push(X);
    cost[X-1] = 0;
    int current, next;
    double distance;
    while ( not q_graph.empty() ) {
        current = q_graph.front();
        q_graph.pop();
        for ( int i=0; i<list_lines[current-1].size(); i++ ) {
            next = list_lines[current-1][i];
            distance = std::sqrt(
                        ( p[current-1] - p[next-1] ) * ( p[current-1] - p[next-1] )
                      + ( q[current-1] - q[next-1] ) * ( q[current-1] - q[next-1] )
                    );
            if ( cost[next-1] > cost[current-1] + distance ) {
                cost[next-1] = cost[current-1] + distance;
                q_graph.push(next);
            }
            if ( next == Y ) break;
        }

    }

    /* output */
    printf( "%.8lf\n", cost[Y-1] );

    return 0;
}