#include <bits/stdc++.h>
using namespace std;
template <typename T>
inline void read(T &x) {
  x = 0;
  char ch = getchar();
  bool f = false;
  while (!isdigit(ch)) {
    if (ch == '-') {
      f = true;
    }
    ch = getchar();
  }
  while (isdigit(ch)) {
    x = (x << 1) + (x << 3) + (ch ^ 48);
    ch = getchar();
  }
  x = f ? -x : x;
  return;
}
template <typename T>
inline void write(T x) {
  if (x < 0) putchar('-'), x = -x;
  if (x > 9) write(x / 10);
  putchar(x % 10 ^ 48);
  return;
}
const int N = 2e5 + 5, M = 4e5 + 5;
long long ans;
int n, m, qq;
int head[N], nex[M], to[M], num[M], idx = 1;
long long val[M];
long long disS[N], disT[N], minn[N << 4];
int from[M], arr[M];
long long len[M];
int las[N], ind[M], cnt, l[N], r[N];
void add(int id, int u, int v, long long w) {
  nex[++idx] = head[u];
  num[idx] = id;
  to[idx] = v;
  val[idx] = w;
  head[u] = idx;
  return;
}
priority_queue<pair<long long, int>, vector<pair<long long, int> >,
               greater<pair<long long, int> > >
    q;
bool vis[N], path[N];
void dijkstra(int s, long long dis[], int f = 0) {
  for (int i = 1; i <= n; i++) dis[i] = 1e18;
  dis[s] = 0;
  q.push({0, s});
  while (!q.empty()) {
    pair<long long, int> t = q.top();
    q.pop();
    int x = t.second;
    long long dist = t.first;
    if (dist > dis[x]) continue;
    for (int i = head[x]; i; i = nex[i]) {
      int y = to[i];
      if (dist + val[i] < dis[y]) {
        dis[y] = dist + val[i];
        las[y] = num[i];
        if (f == 1 && !path[y]) l[y] = l[x];
        if (f == 2 && !path[y]) r[y] = r[x];
        q.push({dis[y], y});
      }
    }
  }
  return;
}
void Trace() {
  memset(ind, -1, sizeof(ind));
  path[1] = true;
  l[1] = r[1] = 0;
  int cur = 1;
  for (int i = 1; cur != n; i++) {
    int id = las[cur];
    ind[id] = i;
    cnt++;
    cur = from[id] ^ arr[id] ^ cur;
    path[cur] = true;
    l[cur] = r[cur] = i;
  }
  return;
}
inline void build(int k, int l, int r) {
  minn[k] = 1e18;
  if (l == r) return;
  int mid = (l + r) >> 1;
  build(k << 1, l, mid);
  build(k << 1 | 1, mid + 1, r);
  return;
}
inline void modify(int k, int l, int r, int x, int y, long long v) {
  if (x > y) return;
  if (x <= l && r <= y) {
    minn[k] = min(minn[k], v);
    return;
  }
  int mid = (l + r) >> 1;
  if (x <= mid) modify(k << 1, l, mid, x, y, v);
  if (y > mid) modify(k << 1 | 1, mid + 1, r, x, y, v);
}
inline long long query(int k, int l, int r, int x) {
  if (l == r) return minn[k];
  int mid = (l + r) >> 1;
  long long res = minn[k];
  if (x <= mid)
    res = min(res, query(k << 1, l, mid, x));
  else
    res = min(res, query(k << 1 | 1, mid + 1, r, x));
  return res;
}
int main() {
  read(n), read(m), read(qq);
  for (int i = 1; i <= m; i++) {
    read(from[i]), read(arr[i]), read(len[i]);
    add(i, from[i], arr[i], len[i]);
    add(i, arr[i], from[i], len[i]);
  }
  dijkstra(n, disT);
  Trace();
  dijkstra(1, disS, 1);
  dijkstra(n, disT, 2);
  build(1, 1, cnt);
  for (int i = 1; i <= m; i++) {
    if (ind[i] == -1) {
      modify(1, 1, cnt, l[from[i]] + 1, r[arr[i]],
             disS[from[i]] + len[i] + disT[arr[i]]);
      modify(1, 1, cnt, l[arr[i]] + 1, r[from[i]],
             disS[arr[i]] + len[i] + disT[from[i]]);
    }
  }
  for (int i = 1; i <= qq; i++) {
    int id;
    long long lenth;
    ans = disS[n];
    read(id), read(lenth);
    if (ind[id] != -1) {
      ans = disS[n] - len[id] + lenth;
      if (lenth > len[id]) ans = min(ans, query(1, 1, cnt, ind[id]));
    } else {
      if (lenth < len[id]) {
        ans = min(ans, disS[from[id]] + disT[arr[id]] + lenth);
        ans = min(ans, disS[arr[id]] + disT[from[id]] + lenth);
      }
    }
    write(ans), putchar('\n');
  }
  return 0;
}
