include iostream include iomanip include cstdio include cstring includ

#include <iostream>
#include <iomanip>
#include <cstdio>
#include <cstring>
#include <algorithm>
using namespace std;

typedef long long ll;
typedef long double ld;
#define PATH "D:\\QtProjects\\olymp\\"

const int N = 10001;
const int M = 100000;

int head[N], thead[N];
int linke[M];
int cap[M];
int dest[M];
int sz;
int used[N];
int curused;
inline void init(){
  memset(linke, -1, sizeof(linke));
  memset(head, -1,  sizeof(head));
  memset(used, -1, sizeof(used));
  //fill(linke, linke + M, -1);
  //fill(head, head + N, -1);
  //fill(used, used + N, -1);
  curused = 0;
  sz = 0;
}

inline void addarc(const int frm, const int to, const int capacity){
  dest[sz] = to;
  linke[sz] = head[frm];
  head[frm] = sz;
  cap[sz] = capacity;
  ++sz;
}

inline void addedge(const int frm, const int to, const int capacity){
  addarc(frm, to, capacity);
  addarc(to, frm, 0);
}

int S, T;
int lvl[N];

inline int dfs(int v, int f){
  if (v == T) return f;

  int ans = 0;
  for (int& arc = thead[v]; arc != -1 && f > 0; arc = linke[arc]){
    int u = dest[arc];
    if (cap[arc] && lvl[u] == lvl[v] + 1){
      int curf = dfs(u, min(f, cap[arc]));
        if (curf){
          cap[arc] -= curf;
          cap[arc ^ 1] += curf;
          //return curf;
          f -= curf;
          ans += curf;
        }
    }
  }
  return ans;
}
const int INF = 2e9;

int q[N + 5];
inline bool bfs(const int mCap = 1){

  int l = 0;
  int r = 1;
  memset(lvl, -1, sizeof(lvl));
  lvl[S] = 0;
  //from[S] = -1;
  q[0] = S;

  while (l != r){
    int v = q[l++];
    //int v = q.front(); q.pop();
    for (int arc = head[v]; arc != -1; arc = linke[arc]){
      int u = dest[arc];
      if (cap[arc] >= mCap && lvl[u] == -1){
        //from[u] = arc;
        lvl[u] = lvl[v] + 1;
        q[r++] = u;
      }
    }
  }
  return lvl[T] != -1;
}


int main(){
  freopen(PATH"input.txt", "r", stdin);
  //freopen("partition.in", "r", stdin);
  //freopen("partition.out", "w", stdout);
  //ios_base::sync_with_stdio(false);
  init();
  int n; scanf("%d\n", &n);
  S = 0; T = n - 1;
  for (int i = 0, t1, t2; i < n; ++i) scanf("%d%d", &t1, &t2);

  int m; scanf("%d", &m);
  for (int i = 0; i < m; ++i){
    int a, b, c;
    scanf("%d%d%d", &a, &b, &c);
    //cin >> a >> b >> c;
    --a; --b;
    addarc(a, b, c);
    addarc(b, a, c);
  }

  int sum = 0;
  while (bfs()){
    memcpy(thead, head, sizeof(head));
    for (int t = dfs(S, INF); t != 0; t = dfs(S, INF)){
      //++curused;
      sum += t;
    }
  }

  printf("%d\n", sum);
  for (int arc = 0; arc < sz; arc += 2){
    if (cap[arc] < cap[arc ^ 1]){
      int to = dest[arc] + 1;
      int fr = dest[arc ^ 1] + 1;
      int f = (cap[arc ^ 1] - cap[arc]) / 2;
      printf("%d %d %d\n", fr, to, f);
      //cout << fr << ' ' << to << ' ' << f << '\n';
    }
    else
    {
      int to = dest[arc ^ 1] + 1;
      int fr = dest[arc] + 1;
      int f = (cap[arc] - cap[arc ^ 1]) / 2;
      printf("%d %d %d\n", fr, to, f);
      //cout << fr << ' ' << to << ' ' << f << '\n';
    }
  }
  //cout.flush();

  return 0;
}