#include <iostream>
#include <cstdio>
#include <cstring>
#include <algorithm>
#include <vector>
#define ll long long
#define inf 5000000000000000000ll
using namespace std;
ll read(){
	ll x=0;
	char ch=getchar();
	while(ch<'0'||ch>'9')ch=getchar();
	while(ch>='0'&&ch<='9')x=x*10+ch-'0',ch=getchar();
	return x;
}
void write(ll x){
	if (x<10){
		putchar(x+'0');
		return;
	}
	write(x/10);
	putchar(x%10+'0');
	return;
}
int n,m,q;
int u[400005],v[400005],first[200005],nxt[400005];
ll a[200005],w[400005];
struct node{
	int c,s,t,l;
}d[200005];
int fa[200005],sz[200005],son[200005];
ll depth[200005];
void dfs1(int now,int f,ll d){
	fa[now]=f,depth[now]=d;
	sz[now]=1;
	son[now]=0;
	for (int i=first[now];i;i=nxt[i])
		if (v[i]!=f){
			dfs1(v[i],now,d+w[i]);
			sz[now]+=sz[v[i]];
			if (son[now]==0||sz[v[i]]>sz[son[now]])son[now]=v[i];
		}
	return;
}
int top[200005],idx,dfn[200005],nfd[200005],dfo[200005];
void dfs2(int now,int f,int t){
	top[now]=t;
	dfn[now]=++idx;
	nfd[idx]=now;
	if (son[now]!=0)dfs2(son[now],now,t);
	for (int i=first[now];i;i=nxt[i])
		if (v[i]!=f&&v[i]!=son[now])dfs2(v[i],now,v[i]);
	dfo[now]=idx;
	return;
}
int lca(int a,int b){
	while(top[a]!=top[b]){
		if (depth[top[a]]<depth[top[b]])swap(a,b);
		a=fa[top[a]];
	}
	if (depth[a]>depth[b])swap(a,b);
	return a;
}
ll dis(int a,int b){
	return depth[a]+depth[b]-2*depth[lca(a,b)];
}
ll ans[200005];
namespace Case1{
	void work(){
		for (int i=1;i<=q;i++){
			for (int j=1;j<=n;j++)
				ans[i]=min(ans[i],2*dis(d[i].l,j)+a[j]*d[i].c);
		}
		return;
	}
}
namespace Case2{
	ll ask(int c,int l,int r){
		ll ans=inf;
		for (int i=l;i<=r;i++){
			int x=nfd[i];
			ans=min(ans,2*depth[x]+a[x]*c);
		}
		return ans;
	}
	void work(){
		for (int i=1;i<=q;i++){
			int x=d[i].s;
			while(x!=0&&depth[x]>depth[d[i].l]){
				ans[i]=min(ans[i],ask(d[i].c,dfn[x],dfo[x])-2*depth[d[i].l]);
				x=fa[top[x]];
			}
			x=d[i].t;
			while(x!=0&&depth[x]>depth[d[i].l]){
				ans[i]=min(ans[i],ask(d[i].c,dfn[x],dfo[x])-2*depth[d[i].l]);
				x=fa[top[x]];
			}
		}
		return;
	}
}
namespace Case3{
	vector<pair<ll,ll>> qwq[200005];
	ll ask(int c,int l,int r){
		ll ans=inf;
		for (int i=l;i<=r;i++)
			for (int j=0;j<(int)qwq[i].size();j++)
				ans=min(ans,qwq[i][j].second+qwq[i][j].first*c);
		return ans;
	}
	void work(){
		for (int i=1;i<=n;i++){
			int x=i;
			while(x!=0)qwq[dfn[x]].push_back(make_pair(a[i],2*(depth[i]-depth[x]))),x=fa[top[x]];
		}
		for (int i=1;i<=q;i++){
			int x=d[i].s;
			while(x!=0&&depth[x]>depth[d[i].l]){
				ans[i]=min(ans[i],ask(d[i].c,max(dfn[top[x]],dfn[d[i].l]),dfn[x]));
				x=fa[top[x]];
			}
			x=d[i].t;
			while(x!=0&&depth[x]>depth[d[i].l]){
				ans[i]=min(ans[i],ask(d[i].c,max(dfn[top[x]],dfn[d[i].l]),dfn[x]));
				x=fa[top[x]];
			}
		}
		return;
	}
}
int main(){
	n=read(),m=read(),q=read();
	for (int i=1;i<=n;i++)a[i]=read();
	for (int i=1;i<n;i++){
		u[i]=read(),v[i]=read(),w[i]=read();
		nxt[i]=first[u[i]],first[u[i]]=i;
		u[i+n]=v[i],v[i+n]=u[i],w[i+n]=w[i];
		nxt[i+n]=first[u[i+n]],first[u[i+n]]=i+n;
	}
	dfs1(1,0,0);
	dfs2(1,0,1);
	for (int i=1;i<=q;i++){
		ll x=read(),y=read();
		d[i].s=x%n,d[i].t=y%n;
		if (d[i].s==0)d[i].s=n;
		if (d[i].t==0)d[i].t=n;
		d[i].l=lca(d[i].s,d[i].t);
		if (x<y)swap(x,y);
		d[i].c=(x-1)/n-(y-1)/n;
	}
	for (int i=1;i<=q;i++)ans[i]=inf;
	Case1::work();
	Case2::work();
	Case3::work();
	for (int i=1;i<=q;i++)write(ans[i]+depth[d[i].s]+depth[d[i].t]-2*depth[d[i].l]),putchar('\n');
	return 0;
}