#include <bits/stdc++.h>
using namespace std;
const int MAXN = 305;
int fa[MAXN], a[MAXN], b[MAXN], stk[MAXN], sz;
int head[MAXN], edge[MAXN << 1], next1[MAXN << 1], esz;
vector<pair<int, pair<int, int> > > ans;
int mfind(int x) {
  if (x == fa[x]) return x;
  return fa[x] = mfind(fa[x]);
}
void addedge(int u, int v) {
  edge[esz] = v;
  next1[esz] = head[u];
  head[u] = esz++;
}
int dfs(int u, int p, int t) {
  stk[sz++] = u;
  if (u == t) return 1;
  for (int i = head[u]; i + 1; i = next1[i]) {
    int v = edge[i];
    if (v == p) continue;
    if (dfs(v, u, t)) return 1;
  }
  sz--;
  return 0;
}
void call(int last, int flow) {
  if (last == 0) {
    ans.push_back(make_pair(stk[0], make_pair(stk[1], flow)));
    return;
  }
  if (a[stk[last]] < flow) {
    ans.push_back(make_pair(stk[last], make_pair(stk[last + 1], a[stk[last]])));
    call(last - 1, flow);
    ans.push_back(
        make_pair(stk[last], make_pair(stk[last + 1], flow - a[stk[last]])));
  } else {
    ans.push_back(make_pair(stk[last], make_pair(stk[last + 1], flow)));
    call(last - 1, flow);
  }
}
int main() {
  int n, v, e;
  memset(head, -1, sizeof(head));
  scanf("%d%d%d", &n, &v, &e);
  for (int i = 1; i <= n; i++) fa[i] = i;
  for (int i = 1; i <= n; i++) scanf("%d", &a[i]);
  for (int i = 1; i <= n; i++) scanf("%d", &b[i]);
  for (int i = 0; i < e; i++) {
    int u, v;
    scanf("%d%d", &u, &v);
    int uu = mfind(u);
    int vv = mfind(v);
    if (uu != vv) {
      fa[uu] = vv;
      addedge(u, v);
      addedge(v, u);
    }
  }
  for (int i = 1; i <= n; i++) {
    for (int j = 1; j <= n; j++) {
      if (a[i] > b[i] && a[j] < b[j]) {
        int res = min(a[i] - b[i], b[j] - a[j]);
        int ok = dfs(i, 0, j);
        if (ok == 0) continue;
        call(sz - 2, res);
        a[i] -= res;
        a[j] += res;
        sz = 0;
      }
    }
  }
  for (int i = 1; i <= n; i++)
    if (a[i] != b[i]) {
      printf("NO\n");
      return 0;
    }
  int k = ans.size();
  printf("%d\n", k);
  for (int i = 0; i < k; i++) {
    printf("%d %d %d\n", ans[i].first, ans[i].second.first,
           ans[i].second.second);
  }
  return 0;
}
