#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;

// a + b x
// b: decreasing
// x: increasing
struct Cht {
  int head;
  vector<pair<Int, Int>> ps;
  Cht() : head(0) {}
  void add(Int a, Int b) {
    for (; (int)ps.size() - head >= 2; ps.pop_back()) {
      const Int a2 = ps[ps.size() - 2].first, b2 = ps[ps.size() - 2].second;
      const Int a1 = ps[ps.size() - 1].first, b1 = ps[ps.size() - 1].second;
      if ((__int128)(a1 - a2) * (b1 - b) < (__int128)(a - a1) * (b2 - b1)) break;
    }
    ps.emplace_back(a, b);
// cerr<<"ps = "<<ps<<endl;
  }
  Int get(Int x) {
    for (; (int)ps.size() - head >= 2 && ps[head].first + ps[head].second * x >= ps[head + 1].first + ps[head + 1].second * x; ++head) {}
    if ((int)ps.size() - head == 0) return INF;
    return ps[head].first + ps[head].second * x;
  }
};

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


namespace sub3 {
vector<int> dep;
vector<Int> cs;
void dfs(int u, int p, int d, Int c) {
  dep[u] = d;
  cs[u] = c;
  for (const int i : G[u]) {
    const int v = A[i] ^ B[i] ^ u;
    if (p != v) {
      dfs(v, u, d + 1, c + C[i]);
    }
  }
}
int segN;
vector<Cht> segs[3];
Int get(int h, int a, int b, Int x) {
  Int ret = INF;
  for (a += segN, b += segN; a < b; a >>= 1, b >>= 1) {
    if (a & 1) chmin(ret, segs[h][a++].get(x));
    if (b & 1) chmin(ret, segs[h][--b].get(x));
  }
  return ret;
}
vector<Int> run() {
  dep.assign(N, -1);
  cs.assign(N, 0);
  for (int u = 0; u < N; ++u) if (G[u].size() == 1) {
    dfs(u, -1, 0, 0);
    break;
  }
// cerr<<"dep = "<<dep<<", cs = "<<cs<<endl;
  for (segN = 1; segN < N; segN <<= 1) {}
  for (int h = 0; h < 3; ++h) {
    segs[h].assign(segN << 1, Cht());
  }
  {
    vector<int> us(N);
    for (int u = 0; u < N; ++u) us[u] = u;
    sort(us.begin(), us.end(), [&](int u, int v) -> bool {
      return (D[u] > D[v]);
    });
    for (const int u : us) {
      for (int a = segN + dep[u]; a; a >>= 1) {
        segs[0][a].add(- cs[u] - cs[u], D[u]);
        segs[1][a].add(+ cs[u] - cs[u], D[u]);
        segs[2][a].add(+ cs[u] + cs[u], D[u]);
      }
    }
  }
  vector<Int> ans(Q, INF);
  {
    vector<int> qs(Q);
    for (int q = 0; q < Q; ++q) qs[q] = q;
    sort(qs.begin(), qs.end(), [&](int q0, int q1) -> bool {
      return (L[q0] < L[q1]);
    });
    for (const int q : qs) {
      int s = S[q], t = T[q];
      int x = dep[s], y = dep[t];
      if (x > y) {
        swap(s, t);
        swap(x, y);
      }
      chmin(ans[q], + cs[s] + get(0, 0, x,     L[q]) + cs[t]);
      chmin(ans[q], - cs[s] + get(1, x, y + 1, L[q]) + cs[t]);
      chmin(ans[q], - cs[s] + get(2, y + 1, N, L[q]) - cs[t]);
    }
  }
  return ans;
}
}  // sub3


namespace sub4 {
vector<Int> run() {
  int r = -1;
  for (int u = 0; u < N; ++u) if ((int)G[u].size() == N - 1) {
    r = u;
    break;
  }
  vector<Int> cs(N, 0);
  for (int i = 0; i < N - 1; ++i) {
    cs[A[i] ^ B[i] ^ r] = C[i];
  }
// cerr<<"r = "<<r<<", cs = "<<cs<<endl;
  Cht cht;
  {
    vector<int> us(N);
    for (int u = 0; u < N; ++u) us[u] = u;
    sort(us.begin(), us.end(), [&](int u, int v) -> bool {
      return (D[u] > D[v]);
    });
    for (const int u : us) {
      cht.add(2 * cs[u], D[u]);
    }
  }
  vector<Int> ans(Q, INF);
  {
    vector<int> qs(Q);
    for (int q = 0; q < Q; ++q) qs[q] = q;
    sort(qs.begin(), qs.end(), [&](int q0, int q1) -> bool {
      return (L[q0] < L[q1]);
    });
    for (const int q : qs) {
      if (S[q] == T[q]) {
        chmin(ans[q], D[S[q]] * L[q]);
      } else {
        chmin(ans[q], D[S[q]] * L[q] + cs[S[q]] + cs[T[q]]);
        chmin(ans[q], cs[S[q]] + cs[T[q]] + D[T[q]] * L[q]);
      }
      chmin(ans[q], cs[S[q]] + cht.get(L[q]) + cs[T[q]]);
    }
  }
  return ans;
}
}  // sub4


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);
    }
    
    vector<int> freqDeg(N, 0);
    for (int u = 0; u < N; ++u) {
      ++freqDeg[G[u].size()];
    }
    
    vector<Int> ans;
    if (freqDeg[N - 1] >= 1) {
      ans = sub4::run();
    } else if (freqDeg[1] <= 2) {
      ans = sub3::run();
    } else {
      ans = brute::run();
    }
    for (int q = 0; q < Q; ++q) {
      printf("%lld\n", ans[q]);
    }
#ifdef LOCAL
const auto brt=brute::run();
cerr<<"brt = "<<brt<<endl;
cerr<<"ans = "<<ans<<endl;
assert(brt==ans);
#endif
  }
  return 0;
}