#include <bits/stdc++.h>
using namespace std;
const int N = 300005;
const long long inf = 1e18;
long long dis[3][N], t[N * 4];
bool on[N];
int idx[N], lstvis[N], tot, l[N], r[N], n, m, Q;
int head[N], cnt;
struct edge {
  int u, v, d;
} a[N];
struct e {
  int id, next, to;
  long long dis;
} edge[N * 2];
struct node {
  int pos;
  long long dis;
  bool operator<(const node &x) const { return x.dis < dis; }
};
priority_queue<node> q;
inline int read() {
  int x = 0, f = 1;
  char ch = getchar();
  while (!isdigit(ch)) {
    if (ch == '-') f = -1;
    ch = getchar();
  }
  while (isdigit(ch)) {
    x = x * 10 + ch - '0';
    ch = getchar();
  }
  return x * f;
}
inline void add(int id, int from, int to, long long dis) {
  edge[++cnt].id = id;
  edge[cnt].next = head[from];
  edge[cnt].to = to;
  edge[cnt].dis = dis;
  head[from] = cnt;
}
inline void dijkstra(int s, int op, int f) {
  for (int i = 1; i <= n; i++) dis[op][i] = inf;
  dis[op][s] = 0;
  q.push((node){s, 0});
  while (!q.empty()) {
    node fa = q.top();
    q.pop();
    int x = fa.pos;
    if (fa.dis > dis[op][x]) continue;
    for (int i = head[x]; i; i = edge[i].next) {
      int to = edge[i].to;
      if (dis[op][to] > fa.dis + edge[i].dis) {
        dis[op][to] = fa.dis + edge[i].dis;
        lstvis[to] = edge[i].id;
        if (f == 1 && !on[to]) l[to] = l[x];
        if (f == 2 && !on[to]) r[to] = r[x];
        q.push((node){to, dis[op][to]});
      }
    }
  }
}
inline void pre_work() {
  on[1] = 1;
  l[1] = r[1] = 0;
  int cur = 1;
  for (int i = 1; cur != n; i++) {
    int id = lstvis[cur];
    idx[id] = i;
    ++tot;
    cur = a[id].u ^ a[id].v ^ cur;
    on[cur] = 1;
    l[cur] = r[cur] = i;
  }
}
inline void build(int k, int l, int r) {
  t[k] = inf;
  if (l == r) return;
  int mid = (l + r) >> 1;
  build(k * 2, l, mid);
  build(k * 2 + 1, mid + 1, r);
}
inline void update(int k, int l, int r, int ql, int qr, long long v) {
  if (ql > qr) return;
  if (ql <= l && r <= qr) {
    t[k] = min(t[k], v);
    return;
  }
  int mid = (l + r) >> 1;
  if (ql <= mid) update(k * 2, l, mid, ql, qr, v);
  if (qr > mid) update(k * 2 + 1, mid + 1, r, ql, qr, v);
}
inline long long query(int k, int l, int r, int x) {
  if (l == r) return t[k];
  int mid = (l + r) >> 1;
  long long res = t[k];
  if (x <= mid)
    res = min(res, query(k * 2, l, mid, x));
  else
    res = min(res, query(k * 2 + 1, mid + 1, r, x));
  return res;
}
signed main() {
  n = read();
  m = read();
  Q = read();
  for (int i = 1; i <= m; i++) {
    a[i].u = read(), a[i].v = read(), a[i].d = read();
    add(i, a[i].u, a[i].v, a[i].d);
    add(i, a[i].v, a[i].u, a[i].d);
    idx[i] = -1;
  }
  dijkstra(n, 1, 0);
  pre_work();
  dijkstra(1, 0, 1);
  dijkstra(n, 1, 2);
  build(1, 1, tot);
  for (int i = 1; i <= m; i++) {
    if (idx[i] == -1) {
      update(1, 1, tot, l[a[i].u] + 1, r[a[i].v],
             dis[0][a[i].u] + dis[1][a[i].v] + a[i].d);
      update(1, 1, tot, l[a[i].v] + 1, r[a[i].u],
             dis[0][a[i].v] + dis[1][a[i].u] + a[i].d);
    }
  }
  while (Q--) {
    long long ans = dis[0][n];
    int id = read(), len = read();
    if (idx[id] != -1) {
      ans = dis[0][n] - a[id].d + len;
      if (len > a[id].d) {
        ans = min(ans, query(1, 1, tot, idx[id]));
      }
    } else {
      if (len < a[id].d) {
        ans = min(ans, dis[0][a[id].u] + len + dis[1][a[id].v]);
        ans = min(ans, dis[0][a[id].v] + len + dis[1][a[id].u]);
      }
    }
    printf("%lld\n", ans);
  }
  return 0;
}
