var f:array[..,..]of longint;

     head,vet,next,dep,fa,val,x,y,z,a,b,r,cnt,size,len,c,dis:array[..]of longint;

     n,m,i,left,right,mid,last,tot,tmp,maxw,maxans:longint;

 procedure add(a,b,c:longint);

 begin

  inc(tot);

  next[tot]:=head[a];

  vet[tot]:=b;

  len[tot]:=c;

  head[a]:=tot;

 end;

 procedure dfs(u,father:longint);

 var e,v,i:longint;

 begin

  for i:= to  do

  begin

   if dep[u]<<<i then break;

   f[u,i]:=f[f[u,i-],i-];

  end;

  size[u]:=;

  e:=head[u];

  while e<> do

  begin

   v:=vet[e];

   if v<>fa[u] then

   begin

    f[v,]:=u;

    fa[v]:=u;

    dep[v]:=dep[u]+;

    dis[v]:=dis[u]+len[e];

    dfs(v,u);

    size[u]:=size[u]+size[v];

   end;

   e:=next[e];

  end;

 end;

 procedure swap(var x,y:longint);

 var t:longint;

 begin

  t:=x; x:=y; y:=t;

 end;

 function lca(x,y:longint):longint;

 var i,d:longint;

 begin

  if dep[x]<dep[y] then swap(x,y);

  d:=dep[x]-dep[y];

  for i:= to  do

   if d and (<<i)> then x:=f[x,i];

  for i:= downto  do

   if f[x,i]<>f[y,i] then

   begin

    x:=f[x,i]; y:=f[y,i];

   end;

  if x=y then exit(x);

  exit(f[x,]);

 end;

 function max(x,y:longint):longint;

 begin

  if x>y then exit(x);

  exit(y);

 end;

 function dfs2(u:longint):longint;

 var e,v:longint;

 begin

  e:=head[u];

  while e<> do

  begin

   v:=vet[e];

   if v<>fa[u] then cnt[u]:=cnt[u]+dfs2(v);

   e:=next[e];

  end;

  if cnt[u]=tmp then maxw:=max(maxw,val[u]);

  exit(cnt[u]);

 end;

 function isok(k:longint):boolean;

 var i:longint;

 begin

  maxans:=; maxw:=; tmp:=;

  fillchar(cnt,sizeof(cnt),);

  for i:= to n do

   if c[i]>k then

   begin

    maxans:=max(maxans,c[i]);

    inc(cnt[a[i]]);

    inc(cnt[b[i]]);

    cnt[r[i]]:=cnt[r[i]]-;

    inc(tmp);

   end;

  dfs2();

  if maxans-maxw<=k then exit(true);

  exit(false);

 end;

 begin

  readln(n,m);

  for i:= to n- do

  begin

   readln(x[i],y[i],z[i]);

   add(x[i],y[i],z[i]);

   add(y[i],x[i],z[i]);

  end;

  dfs(,);

  for i:= to m do

  begin

   readln(a[i],b[i]);

   r[i]:=lca(a[i],b[i]);

   c[i]:=dis[a[i]]+dis[b[i]]-dis[r[i]]*;

  end;

  for i:= to n- do

   if dep[x[i]]>dep[y[i]] then val[x[i]]:=z[i]

    else val[y[i]]:=z[i];

  left:=; right:=;

  while left<=right do

  begin

   mid:=(left+right)>>;

   if isok(mid) then begin last:=mid; right:=mid-; end

    else left:=mid+;

  end;

  writeln(last);

 end.