import sys
input = sys.stdin.readline
from heapq import heappop, heappush

def main():
    N, M = map( int, input().split())
    X, Y = map( int, input().split())
    X -= 1
    Y -= 1
    PQ = [ tuple( map( int, input().split())) for _ in range(N)]
    E = [[] for _ in range(N)]
    for _ in range(M):
        p, q = map( lambda x: int(x)-1, input().split())
        E[p].append((q, ((PQ[p][0]-PQ[q][0])**2 + (PQ[p][1]-PQ[q][1])**2)**(1/2)))
        E[q].append((p, ((PQ[p][0]-PQ[q][0])**2 + (PQ[p][1]-PQ[q][1])**2)**(1/2)))
    h = [(0,X)]
    V = [-1 for _ in range(N)]
    # W = [False for _ in range(N)]
    # V[X] = 0
    # W[X] = True

    while h:
        d, v = heappop(h)
        if V[v] == -1:
            V[v] = d
        else:
            continue
        for w, e in E[v]:
            if V[w] == -1:
                heappush(h, (d+e, w))
        # print(h)
    print(V[Y])
if __name__ == '__main__':
    main()