#include<cstdio>
#include<vector>
#include<queue>
#include<cstring>
using namespace std;
typedef long long LL;
const LL INF=2e12+5;
const int MAXN=405;
int has[MAXN],sz[MAXN],F,P,tot;
LL dis[MAXN][MAXN];
struct dinic
{
    struct Edge
    {
        int from,to,cap,flow;
        Edge(){}
        Edge(int u,int v,int c,int f):from(u),to(v),cap(c),flow(f){};
    };
    int s,t,d[MAXN],cur[MAXN];
    bool vis[MAXN];
    vector<Edge>edges;
    vector<int>G[MAXN];
    inline void init()
    {
        for(int i=0;i<=2*F+1;i++)G[i].clear();
        edges.clear();
    }
    void addedge(int from,int to,int cap)
    {
        edges.push_back((Edge){from,to,cap,0});
        edges.push_back((Edge){to,from,0,0});
        int m=edges.size();
        G[from].push_back(m-2);
        G[to].push_back(m-1);
    }
    bool bfs()
    {
        memset(vis,0,sizeof(vis));
        queue<int>q;
        q.push(s);
        d[s]=0;
        vis[s]=1;
        while(!q.empty())
        {
            int x=q.front();q.pop();
            for(int i=0;i<G[x].size();i++)
            {
                Edge& e=edges[G[x][i]];
                if(!vis[e.to]&&e.cap>e.flow)
                {
                    vis[e.to]=1;
                    d[e.to]=d[x]+1;
                    q.push(e.to);
                }
            }
        }
        return vis[t];
    }
    int dfs(int x,int a)
    {
        if(x==t||a==0)return a;
        int flow=0,f;
        for(int& i=cur[x];i<G[x].size();i++)
        {
            Edge& e=edges[G[x][i]];
            if(d[x]+1==d[e.to]&&(f=dfs(e.to,min(a,e.cap-e.flow)))>0)
            {
                e.flow+=f;
                edges[G[x][i]^1].flow-=f;
                flow+=f;
                a-=f;
                if(a==0)break;
            }
        }
        return flow;
    }
    int maxflow(int s,int t)
    {
        this->s=s,this->t=t;
        int flow=0;
        while(bfs())
        {
            memset(cur,0,sizeof(cur));
            flow+=dfs(s,2e5+5);
        }
        return flow;
    }
}dc;
void floyd()
{
    for(int k=1;k<=F;k++)
        for(int i=1;i<=F;i++)
            for(int j=1;j<=F;j++)
                dis[i][j]=min(dis[i][j],dis[i][k]+dis[k][j]);
}
bool jud(LL T)
{
    dc.init();
    for(int i=1;i<=F;i++)
        for(int j=1;j<=F;j++)
            if(dis[i][j]<=T)
                dc.addedge(i,j+F,2e5+5);
    for(int i=1;i<=F;i++)
        dc.addedge(0,i,has[i]),dc.addedge(i+F,2*F+1,sz[i]);
    return tot==dc.maxflow(0,2*F+1);
}
int main()
{
    scanf("%d%d",&F,&P);
    for(int i=1;i<=F;i++)
        scanf("%d%d",&has[i],&sz[i]),tot+=has[i];
    for(int i=1;i<=F;i++)
        for(int j=1;j<=F;j++)
            dis[i][j]=(i==j?0:INF);
    for(int i=1;i<=P;i++)
    {
        int u,v,w;
        scanf("%d%d%d",&u,&v,&w);
        dis[u][v]=dis[v][u]=min(dis[u][v],1LL*w);
    }
    floyd();
    LL l=-1,r=INF,ans=-1;
    while(l<r)
    {
        LL mid=(l+r)/2;
        if(jud(mid))ans=r=mid;
        else l=mid+1;
    }
    printf("%lld\n",ans);
    return 0;
}