#include<iostream>

#include<cstdio>

#include<cstring>

#include<queue>

using namespace std;

int const maxn=2e4+,maxm=2e5+,inf=0x3f3f3f3f;

int n,m,hd[maxn],d[maxn],ct=,cur[maxn],ans;

queue<int>q;

struct N{

    int to,nxt,w;

    N(int t=,int n=,int w=):to(t),nxt(n),w(w) {}

}ed[(maxn+maxm)<<];

void add(int x,int y,int z)

{

    ed[++ct]=N(y,hd[x],z); hd[x]=ct;

    ed[++ct]=N(x,hd[y],); hd[y]=ct;

}

bool bfs()

{

    while(q.size())q.pop();

    memset(d,,sizeof d);

    q.push(); d[]=;

    while(q.size())

    {

        int x=q.front(); q.pop();

        for(int i=hd[x],u;i;i=ed[i].nxt)

            if(!d[u=ed[i].to]&&ed[i].w)d[u]=d[x]+,q.push(u);

    }

    return d[n+];

}

int dfs(int x,int f)

{

    if(x==n+)return f;

    int res=;

    for(int &i=cur[x],u;i;i=ed[i].nxt)

    {

        if(d[u=ed[i].to]==d[x]+&&ed[i].w)

        {

            int k=dfs(u,min(ed[i].w,f-res));//f-res!!!

            res+=k; ed[i].w-=k; ed[i^].w+=k;

            if(res==f)return f;

        }

    }

    if(!res)d[x]=;

    return res;

}

int main()

{

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

    for(int i=,a,b;i<=n;i++)

    {

        scanf("%d%d",&a,&b);

        add(,i,a); add(i,n+,b);

    }

    for(int i=,x,y,z;i<=m;i++)

    {

        scanf("%d%d%d",&x,&y,&z);

        add(x,y,z); add(y,x,z);

    }

    while(bfs())

    {

        memcpy(cur,hd,sizeof hd);

        ans+=dfs(,inf);

    }

    printf("%d",ans);

    return ;

}