#include <bits/stdc++.h>
using namespace std;
template <typename T1, typename T2>
inline void chkmin(T1 &x, T2 y) {
  if (x > y) x = y;
}
template <typename T1, typename T2>
inline void chkmax(T1 &x, T2 y) {
  if (x < y) x = y;
}
inline int readChar();
template <class T = int>
inline T readInt();
template <class T>
inline void writeInt(T x, char end = 0);
inline void writeChar(int x);
inline void writeWord(const char *s);
static const int buf_size = 4096;
inline int getChar() {
  static char buf[buf_size];
  static int len = 0, pos = 0;
  if (pos == len) {
    pos = 0, len = fread(buf, 1, buf_size, stdin);
  }
  if (pos == len) {
    return -1;
  }
  return buf[pos++];
}
inline int readChar() {
  int c = getChar();
  while (c <= 32) {
    c = getChar();
  }
  return c;
}
template <class T>
inline T readInt() {
  int s = 1, c = readChar();
  T x = 0;
  if (c == '-') s = -1, c = getChar();
  while ('0' <= c && c <= '9') x = x * 10 + c - '0', c = getChar();
  return s == 1 ? x : -x;
}
static int write_pos = 0;
static char write_buf[buf_size];
inline void writeChar(int x) {
  if (write_pos == buf_size)
    fwrite(write_buf, 1, buf_size, stdout), write_pos = 0;
  write_buf[write_pos++] = x;
}
template <class T>
inline void writeInt(T x, char end) {
  if (x < 0) writeChar('-'), x = -x;
  char s[24];
  int n = 0;
  while (x || !n) s[n++] = '0' + x % 10, x /= 10;
  while (n--) writeChar(s[n]);
  if (end) writeChar(end);
}
inline void writeWord(const char *s) {
  while (*s) writeChar(*s++);
}
struct Flusher {
  ~Flusher() {
    if (write_pos) fwrite(write_buf, 1, write_pos, stdout), write_pos = 0;
  }
} flusher;
const int MAXN = 305;
vector<int> g[MAXN];
pair<pair<int, int>, int> ans[MAXN * MAXN * 2];
pair<int, int> p[MAXN];
int aa[MAXN], bb[MAXN], f[MAXN], dong[MAXN];
int k;
inline void up(int u, int v, int c) {
  ans[k++] = make_pair(make_pair(u, v), c);
  aa[u] -= c;
  aa[v] += c;
}
void dfs(int x, int need) {
  f[x] = 1;
  for (int i = (int)(g[x]).size() - 1; i >= 0 && aa[x] < need; i--) {
    int j = g[x][i];
    if (f[j]) {
      continue;
    }
    if (dong[j]) {
      int tmp = min(bb[j], need - aa[x]);
      up(j, x, tmp);
      dfs(j, bb[j]);
      if (aa[j] < bb[j]) {
        up(x, j, bb[j] - aa[j]);
      }
    } else {
      dfs(j, need);
      int limit = min(aa[j], need - aa[x]);
      up(j, x, limit);
    }
  }
}
int main() {
  int n = readInt(), v = readInt(), m = readInt();
  for (int i = 1; i <= n; i++) {
    aa[i] = readInt();
  }
  for (int i = 1; i <= n; i++) {
    bb[i] = readInt();
  }
  for (int i = 1; i <= n; i++) {
    p[i - 1] = make_pair(-bb[i], i);
  }
  sort(p, p + n);
  for (int i = 0; i < m; i++) {
    int a = readInt(), b = readInt();
    g[a].push_back(b);
    g[b].push_back(a);
  }
  for (int h = 0; h < n; h++) {
    int i = p[h].second;
    memset(f, 0, sizeof(f));
    dfs(i, bb[i]);
    dong[i] = 1;
  }
  for (int i = 1; i <= n; i++) {
    if (aa[i] != bb[i]) {
      writeWord("NO\n");
      return 0;
    }
  }
  writeInt(k, '\n');
  for (int i = 0; i < k; i++) {
    writeInt(ans[i].first.first, ' ');
    writeInt(ans[i].first.second, ' ');
    writeInt(ans[i].second, '\n');
  }
  return 0;
}
