#include <cassert>
#include <cmath>
#include <cstdint>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <algorithm>
#include <bitset>
#include <complex>
#include <deque>
#include <functional>
#include <iostream>
#include <limits>
#include <map>
#include <numeric>
#include <queue>
#include <set>
#include <sstream>
#include <string>
#include <unordered_map>
#include <unordered_set>
#include <utility>
#include <vector>

using namespace std;

using Int = long long;

template <class T1, class T2> ostream &operator<<(ostream &os, const pair<T1, T2> &a) { return os << "(" << a.first << ", " << a.second << ")"; };
template <class T> ostream &operator<<(ostream &os, const vector<T> &as) { const int sz = as.size(); os << "["; for (int i = 0; i < sz; ++i) { if (i >= 256) { os << ", ..."; break; } if (i > 0) { os << ", "; } os << as[i]; } return os << "]"; }
template <class T> void pv(T a, T b) { for (T i = a; i != b; ++i) cerr << *i << " "; cerr << endl; }
template <class T> bool chmin(T &t, const T &f) { if (t > f) { t = f; return true; } return false; }
template <class T> bool chmax(T &t, const T &f) { if (t < f) { t = f; return true; } return false; }
#define COLOR(s) ("\x1b[" s "m")


constexpr Int INF = 2001001001001001001LL;

Int M;
int N, Q;
vector<Int> D;
vector<int> A, B;
vector<Int> C;
vector<Int> L;
vector<int> S, T;

vector<vector<int>> G;


namespace brute {
Int dist[5010][5010];
void dfs(int r, int u, int p, Int d) {
  dist[r][u] = d;
  for (const int i : G[u]) {
    const int v = A[i] ^ B[i] ^ u;
    if (p != v) {
      dfs(r, v, u, d + C[i]);
    }
  }
}
vector<Int> run() {
  for (int r = 0; r < N; ++r) {
    dfs(r, r, -1, 0);
  }
  vector<Int> ans(Q, INF);
  for (int q = 0; q < Q; ++q) {
    for (int u = 0; u < N; ++u) {
      chmin(ans[q], dist[S[q]][u] + L[q] * D[u] + dist[T[q]][u]);
    }
  }
  return ans;
}
}  // brute


int main() {
  for (; ~scanf("%d%lld%d", &N, &M, &Q); ) {
    D.resize(N);
    for (int u = 0; u < N; ++u) {
      scanf("%lld", &D[u]);
    }
    A.resize(N - 1);
    B.resize(N - 1);
    C.resize(N - 1);
    for (int i = 0; i < N - 1; ++i) {
      scanf("%d%d%lld", &A[i], &B[i], &C[i]);
      --A[i];
      --B[i];
    }
    L.resize(Q);
    S.resize(Q);
    T.resize(Q);
    for (int q = 0; q < Q; ++q) {
      Int s, t;
      scanf("%lld%lld", &s, &t);
      --s;
      --t;
      L[q] = abs(s / N - t / N);
      S[q] = s % N;
      T[q] = t % N;
    }
    
    G.assign(N, {});
    for (int i = 0; i < N - 1; ++i) {
      G[A[i]].push_back(i);
      G[B[i]].push_back(i);
    }
    
    const auto ans = brute::run();
    for (int q = 0; q < Q; ++q) {
      printf("%lld\n", ans[q]);
    }
  }
  return 0;
}