#include<bits/stdc++.h>
using namespace std;
using ll=long long;
using pil=pair<int,ll>;
const int N=5e5+5;
int n,m,q,d[N];ll ds[N];
vector<pil> edge[N];
int ls[N<<1],lg[N<<1];
int f[22][N<<1],ct;
int L[N],R[N],a[N],tg[N];
void dfs(int u,int f)
{
    L[u]=++ct,ls[ct]=u;
    for(auto e:edge[u])
    {
        int v=e.first;
        ll w=e.second;
        if(v==f)continue;
        d[v]=d[u]+1,
        ds[v]=ds[u]+w,
        dfs(v,u);
    }R[u]=++ct,ls[ct]=u;
}int lca(int x,int y)
{
    if(L[x]>L[y])swap(x,y);
    int g=lg[L[y]-L[x]+1];
    int a=f[g][L[x]];
    int b=f[g][R[x]-(1<<g)+1];
    return (d[a]<d[b])?a:b;
}ll dis(int x,int y)
{
    int l=lca(x,y);
    return ds[x]+ds[y]-ds[l]*2;
}int lp[N],rp[N],t=-1;
ll ck(int u,ll t)
{return max(dis(u,lp[t]),dis(u,rp[t]));}
int main()
{
    ios::sync_with_stdio(0);cin.tie(0);cout.tie(0);
    cin>>n>>q;for(int i=1;i<=n;i++)cin>>a[i];
    for(int i=1;i<=n;i++)if(a[i]<n)tg[a[i]]=i;
    while(tg[t+1])t++;
    for(int i=2;i<=n;i++)
    {
        int x,y;ll w;cin>>x>>y>>w;
        edge[x].push_back({y,w});
        edge[y].push_back({x,w});
    }dfs(1,0);m=ct;
    for(int i=2;i<=m;i++)lg[i]=lg[i>>1]+1;
    for(int i=1;i<=m;i++)f[0][i]=ls[i];
    for(int i=1;i<=lg[m];i++)
    for(int j=1;j+(1<<i)-1<=m;j++)
    {
        int x=f[i-1][j];
        int y=f[i-1][j+(1<<i-1)];
        f[i][j]=(d[x]<d[y])?x:y;
    }lp[0]=rp[0]=tg[0];
    for(int c=1;c<=t;c++)
    {
        ll x=dis(lp[c-1],rp[c-1]);
        ll y=dis(lp[c-1],tg[c]);
        ll z=dis(rp[c-1],tg[c]);
        ll mx=max({x,y,z});if(mx==x)
        lp[c]=lp[c-1],rp[c]=rp[c-1];
        else if(mx==y)lp[c]=lp[c-1],
        rp[c]=tg[c];else
        lp[c]=rp[c-1],rp[c]=tg[c];
    }for(int i=1;i<=q;i++)
    {
        int u;ll k;cin>>u>>k;
        int l=0,r=t,mid;
        while(l<r)
        {
            mid=(l+r)>>1;
            if(ck(u,mid+1)<=k)
            l=mid+1;else r=mid;
        }if(ck(u,l)>k)l=-1;
        cout<<l+1<<'\n';
    }
    return 0;
}