#!/usr/bin/env python3
# TODO: Rewrite this O(q n lg n) in C++.
import heapq
from math import dist

n, m, Q = map(int, input().split())
ps = [tuple(map(int, input().split())) for _ in range(n)]
g = [[] for _ in range(n)]
for _ in range(m):
    u, v = map(int, input().split())
    u -= 1
    v -= 1
    g[u].append(v)
    g[v].append(u)

# Process queries
for _ in range(Q):
    c, T = map(int, input().split())
    c -= 1

    # Dijkstra to compute D=sum(sqrt(dist)) to c.
    d = [float("inf")] * n
    d[0] = 0
    q = [(0, 0)]
    while q:
        D, u = heapq.heappop(q)
        if u == c:
            break
        if D > d[u]:
            continue
        for v in g[u]:
            D2 = D + dist(ps[u], ps[v]) ** 0.5
            if D2 < d[v]:
                d[v] = D2
                heapq.heappush(q, (D2, v))

    u -= 1
    D = d[c]
    Q = T / D
    if Q < 2:
        print("impossible")
    else:
        c = Q - (Q**2 - 4) ** 0.5
        print(c * D)