#include <bits/stdc++.h>
using namespace std;
const int maxn = 1e5;
int n, fa[maxn + 2], cont[maxn + 2];
int mx1[maxn + 2], mx2[maxn + 2], diameter[maxn + 2];
bool vist[maxn + 2];
vector<int> G[maxn + 2];
vector<long long> dist[maxn + 2];
map<pair<int, int>, double> Map;
void dfs1(int x, int pre, int col) {
  vist[x] = 1, fa[x] = col;
  int aa[3];
  for (auto nx : G[x]) {
    if (nx == pre) continue;
    dfs1(nx, x, col);
    aa[0] = mx1[nx] + 1, aa[1] = mx1[x], aa[2] = mx2[x];
    sort(aa, aa + 3);
    mx1[x] = aa[2], mx2[x] = aa[1];
  }
}
void dfs2(int x, int pre, vector<long long> &ds, int di) {
  ds.push_back(max(di, mx1[x]));
  for (auto nx : G[x]) {
    if (nx == pre) continue;
    if (mx1[nx] + 1 == mx1[x])
      dfs2(nx, x, ds, max(di, mx2[x]) + 1);
    else
      dfs2(nx, x, ds, max(di, mx1[x]) + 1);
  }
}
int BinSearch(vector<long long> &arr, long long key) {
  int l = 1, r = arr.size() - 1, res = 0;
  while (l <= r) {
    int mid = (l + r) >> 1;
    if (arr[mid] - arr[mid - 1] < key)
      res = mid, l = mid + 1;
    else
      r = mid - 1;
  }
  return res;
}
int main() {
  int m, T, u, v;
  scanf("%d%d%d", &n, &m, &T);
  for (int i = 1; i <= n; ++i) fa[i] = i;
  for (int i = 1; i <= m; ++i) {
    scanf("%d%d", &u, &v);
    G[u].push_back(v);
    G[v].push_back(u);
  }
  for (int i = 1; i <= n; ++i)
    if (!vist[i]) {
      dfs1(i, 0, i);
      dfs2(i, 0, dist[i], 0);
      dist[i].push_back(0);
      sort(dist[i].begin(), dist[i].end());
      diameter[i] = dist[i][dist[i].size() - 1];
      for (int k = 1; k < dist[i].size(); ++k) dist[i][k] += dist[i][k - 1];
    }
  while (T--) {
    scanf("%d%d", &u, &v);
    u = fa[u], v = fa[v];
    if (u == v) {
      printf("%d\n", -1);
      continue;
    }
    if (Map.count(make_pair(u, v))) {
      printf("%f\n", Map[make_pair(u, v)]);
      continue;
    }
    if (dist[u].size() > dist[v].size()) swap(u, v);
    long long mxd = max(diameter[u], diameter[v]), sum = 0;
    for (int i = 1; i < dist[u].size(); ++i) {
      int index = BinSearch(dist[v], mxd - (dist[u][i] - dist[u][i - 1]) - 1);
      sum += (dist[v][dist[v].size() - 1] - dist[v][index]);
      sum += (dist[u][i] - dist[u][i - 1] + 1) * (dist[v].size() - 1 - index);
      sum += mxd * index;
    }
    double ans = double(sum) / (dist[u].size() - 1) / (dist[v].size() - 1);
    Map[make_pair(u, v)] = Map[make_pair(v, u)] = ans;
    printf("%.10f\n", ans);
  }
  return 0;
}
