#include <bits/stdc++.h>
using namespace std;
const int N = 400005;
const long long inf = 1e16;
int n, m, q, te = 1, h[N], nxt[N << 1], fr[N << 1], to[N << 1], mark[N << 1],
             vis[N], cnt, c[N], pre[N], pre_e[N], pos[N], ooe[N], jkk[N];
long long w[N << 1], dis[N], dis1[N], dis2[N], ans[N];
struct node {
  int o;
  long long d;
};
bool operator<(node a, node b) { return a.d > b.d; }
void dij1() {
  for (int i = 1; i <= n; i++) dis[i] = inf, vis[i] = 0, pre[i] = 0;
  dis[1] = 0;
  priority_queue<node> Q;
  Q.push((node){1, 0});
  while (!Q.empty()) {
    int u = Q.top().o;
    Q.pop();
    if (vis[u]) continue;
    vis[u] = 1;
    for (int i = h[u], v; i; i = nxt[i]) {
      v = to[i];
      if (dis[v] > dis[u] + w[i]) {
        dis[v] = dis[u] + w[i];
        pre[v] = u;
        pre_e[v] = i;
        Q.push((node){v, dis[v]});
      }
    }
  }
}
void dij2() {
  for (int i = 1; i <= n; i++) {
    dis1[i] = inf;
    vis[i] = 0;
    if (pos[i])
      ooe[i] = pos[i];
    else
      ooe[i] = 1e9;
  }
  dis1[1] = 0;
  priority_queue<node> Q;
  Q.push((node){1, 0});
  while (!Q.empty()) {
    int u = Q.top().o;
    Q.pop();
    if (vis[u]) continue;
    vis[u] = 1;
    for (int i = h[u], v; i; i = nxt[i]) {
      v = to[i];
      if (dis1[v] > dis1[u] + w[i]) {
        dis1[v] = dis1[u] + w[i];
        if (!pos[v]) ooe[v] = ooe[u];
        Q.push((node){v, dis1[v]});
      } else if (dis1[v] == dis1[u] + w[i]) {
        if (!pos[v]) ooe[v] = min(ooe[v], ooe[u]);
      }
    }
  }
}
void dij3() {
  for (int i = 1; i <= n; i++) {
    dis2[i] = inf;
    vis[i] = 0;
    if (pos[i])
      jkk[i] = pos[i];
    else
      jkk[i] = -1;
  }
  dis2[n] = 0;
  priority_queue<node> Q;
  Q.push((node){n, 0});
  while (!Q.empty()) {
    int u = Q.top().o;
    Q.pop();
    if (vis[u]) continue;
    vis[u] = 1;
    for (int i = h[u], v; i; i = nxt[i]) {
      v = to[i];
      if (dis2[v] > dis2[u] + w[i]) {
        dis2[v] = dis2[u] + w[i];
        if (!pos[v]) jkk[v] = jkk[u];
        Q.push((node){v, dis2[v]});
      } else if (dis2[v] == dis2[u] + w[i]) {
        if (!pos[v]) jkk[v] = max(jkk[v], jkk[u]);
      }
    }
  }
}
long long Tag[N << 2];
void build(int o, int l, int r) {
  Tag[o] = inf;
  if (l == r) return;
  int mid = (l + r) >> 1;
  build((o << 1), l, mid);
  build((o << 1 | 1), mid + 1, r);
}
void Modify(int o, int l, int r, int pl, int pr, long long x) {
  if (l > pr || r < pl) return;
  if (l >= pl && r <= pr) {
    Tag[o] = min(Tag[o], x);
    return;
  }
  int mid = (l + r) >> 1;
  Modify((o << 1), l, mid, pl, pr, x);
  Modify((o << 1 | 1), mid + 1, r, pl, pr, x);
}
void solve(int o, int l, int r, long long mn) {
  mn = min(mn, Tag[o]);
  if (l == r) {
    ans[l] = mn;
    return;
  }
  int mid = (l + r) >> 1;
  solve((o << 1), l, mid, mn);
  solve((o << 1 | 1), mid + 1, r, mn);
}
int main() {
  scanf("%d%d%d", &n, &m, &q);
  for (int i = 1; i <= m; i++) {
    int x, y;
    long long z;
    scanf("%d%d%lld", &x, &y, &z);
    nxt[++te] = h[x];
    h[x] = te;
    fr[te] = x;
    to[te] = y;
    w[te] = z;
    nxt[++te] = h[y];
    h[y] = te;
    fr[te] = y;
    to[te] = x;
    w[te] = z;
  }
  dij1();
  for (int x = n; x; x = pre[x]) {
    c[++cnt] = x;
    if (x != 1) mark[pre_e[x]] = mark[pre_e[x] ^ 1] = pre[x];
  }
  reverse(c + 1, c + 1 + cnt);
  for (int i = 1; i <= cnt; i++) pos[c[i]] = i;
  dij2();
  dij3();
  build(1, 1, cnt);
  for (int i = 2; i <= te; i++)
    if (!mark[i]) {
      int u = fr[i], v = to[i];
      int p = ooe[u], q = jkk[v];
      if (p < q) {
        Modify(1, 1, cnt, p, q - 1, dis1[u] + w[i] + dis2[v]);
      }
    }
  solve(1, 1, cnt, inf);
  while (q--) {
    int e, k;
    scanf("%d%d", &e, &k);
    e <<= 1;
    if (!mark[e])
      printf("%lld\n", min({dis[n], dis1[fr[e]] + k + dis2[to[e]],
                            dis2[fr[e]] + k + dis1[to[e]]}));
    else {
      int x = pos[mark[e]];
      printf("%lld\n", min({ans[x], dis1[fr[e]] + k + dis2[to[e]],
                            dis2[fr[e]] + k + dis1[to[e]]}));
    }
  }
  return 0;
}
