#include<stdio.h>
#include<string.h>
#include<stdlib.h>
#define clr(x)memset(x,0,sizeof(x))
#define INF 0x1f1f1f1f
#define min(a,b)(a)<(b)?(a):(b)
int v[405][405];
int gap[405];
int dis[405];
int c[405][405];
void init(int s,int u,int n)
{int v,x,front=0,rear=0;int q[405];clr(gap);memset(dis,0xff,sizeof(dis));q[rear++]=u;dis[u]=0;while(front<rear){x=q[front++];gap[dis[x]]++;for(v=0;v<=n;v++)if(dis[v]==-1&&c[v][x]>0){dis[v]=dis[x]+1;q[rear++]=v;}}
}
int sap(int s,int u,int n)
{init(s,u,n);int flag,flow=0,top=s,i,j,k;int pre[405];int low[405];while(dis[s]<=n){flag=0;low[s]=INF;for(i=0;i<=n;i++)if(c[top][i]>0&&dis[top]==dis[i]+1&&dis[i]>=0){flag=1;break;}if(flag){low[i]=c[top][i];low[i]=min(low[i],low[top]);pre[i]=top;top=i;if(top==u){flow+=low[u];j=top;while(j!=s){k=pre[j];c[k][j]-=low[u];c[j][k]+=low[u];j=k;}top=s;clr(low);}}else{int dmin=n;for(j=0;j<=n;j++)if(c[top][j]>0&&dis[j]+1<dmin&&dis[j]>=0)dmin=dis[j]+1;gap[dis[top]]--;if(gap[dis[top]]==0)break;gap[dmin]++;dis[top]=dmin;if(top!=s)top=pre[top];}}return flow;
}
long long g[405][405];
int st[202];
int ho[202];
int ok(long long ti,int s,int n,int tot)
{int i,j,flow;clr(c);for(i=1;i<=n;i++){c[s][i]=st[i];c[i+n][n*2+1]=ho[i];}for(i=1;i<=n;i++)for(j=1;j<=n;j++)if(g[i][j]!=-1&&g[i][j]<=ti){c[i][j+n]=INF;c[j][i+n]=INF;}flow=sap(s,2*n+1,2*n+1);if(flow==tot)return 1;return 0;
}
int main()
{int s,t,n,m,i,j,k,a,b,t1,t2;long long low,high,mid,res,w;while(scanf("%d%d",&n,&m)!=EOF){s=0;t1=t2=0;high=0;for(i=1;i<=n;i++){scanf("%d%d",&st[i],&ho[i]);t1+=st[i];t2+=ho[i];}memset(g,-1,sizeof(g));while(m--){scanf("%d%d%lld",&a,&b,&w);if(g[a][b]==-1||w<g[a][b]){//high+=w;g[a][b]=g[b][a]=w;}}if(t1>t2){printf("-1\n");continue;}for(k=1;k<=n;k++)for(i=1;i<=n;i++)if(g[i][k]!=-1)for(j=1;j<=n;j++)if(g[k][j]!=-1&&(g[i][k]+g[k][j]<g[i][j]||g[i][j]==-1))g[i][j]=g[i][k]+g[k][j];for(i=1;i<=n;i++)g[i][i]=0;low=0;high=0;for(i=1;i<=n;i++)for(j=1;j<=n;j++)if(g[i][j]>high)high=g[i][j];res=-1;while(low<=high){mid=(low+high)>>1;if(ok(mid,s,n,t1)){res=mid;high=mid-1;}elselow=mid+1;}printf("%lld\n",res);}return 0;
}