#include<iostream>

 #include<cstdio>

 #include<cstring>

 #include<algorithm>

 #include<queue>

 using namespace std;

 #define MAXN 44444

 #define MAXM 999999

 #define inf 1<<30

 struct Edge {

     int v,cap,next;

 } edge[MAXM];

 int n,m,vs,vt,NE,NV;

 int head[MAXN];

 void Insert(int u,int v,int cap)

 {

     edge[NE].v=v;

     edge[NE].cap=cap;

     edge[NE].next=head[u];

     head[u]=NE++;

     edge[NE].v=u;

     edge[NE].cap=;

     edge[NE].next=head[v];

     head[v]=NE++;

 }

 int level[MAXN];

 int gap[MAXN];

 void bfs(int vt)

 {

     memset(level,-,sizeof(level));

     memset(gap,,sizeof(gap));

     level[vt]=;

     gap[level[vt]]++;

     queue<int>que;

     que.push(vt);

     while(!que.empty()) {

         int u=que.front();

         que.pop();

         for(int i=head[u]; i!=-; i=edge[i].next) {

             int v=edge[i].v;

             if(level[v]!=-)continue;

             level[v]=level[u]+;

             gap[level[v]]++;

             que.push(v);

         }

     }

 }

 int pre[MAXN];

 int cur[MAXN];

 int SAP(int vs,int vt)

 {

     bfs(vt);

     memset(pre,-,sizeof(pre));

     memcpy(cur,head,sizeof(head));

     int u=pre[vs]=vs,flow=,aug=inf;

     gap[]=NV;

     while(level[vs]<NV) {

         bool flag=false;

         for(int &i=cur[u]; i!=-; i=edge[i].next) {

             int v=edge[i].v;

             if(edge[i].cap&&level[u]==level[v]+) {

                 flag=true;

                 pre[v]=u;

                 u=v;

                 //  aug=(aug==-1?edge[i].cap:min(aug,edge[i].cap));

                 aug=min(aug,edge[i].cap);

                 if(v==vt) {

                     flow+=aug;

                     for(u=pre[v]; v!=vs; v=u,u=pre[u]) {

                         edge[cur[u]].cap-=aug;

                         edge[cur[u]^].cap+=aug;

                     }

                     //     aug=-1;

                     aug=inf;

                 }

                 break;

             }

         }

         if(flag)continue;

         int minlevel=NV;

         for(int i=head[u]; i!=-; i=edge[i].next) {

             int v=edge[i].v;

             if(edge[i].cap&&level[v]<minlevel) {

                 minlevel=level[v];

                 cur[u]=i;

             }

         }

         if(--gap[level[u]]==)break;

         level[u]=minlevel+;

         gap[level[u]]++;

         u=pre[u];

     }

     return flow;

 }

 int main()

 {

     int u,v,w,w1,w2;

     scanf("%d%d",&n,&m);

     vs=;

     vt=n+;

     NV=n+;

     NE=;

     memset(head,-,sizeof(head));

     for(int i=; i<=n; i++) {

         scanf("%d%d",&w1,&w2);

         Insert(vs,i,w1);

         Insert(i,vt,w2);

     }

     for(int i=; i<=m; i++) {

         scanf("%d%d%d",&u,&v,&w);

         Insert(u,v,w);

         Insert(v,u,w);

     }

     printf("%d\n",SAP(vs,vt));

     return ;

 }