#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 id,c,s,t,l;
}d[200005];
bool cmp_c(node a,node b){
	return a.c<b.c;
}
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];
struct Vec{
	ll x,y;
	Vec operator -(const Vec &b)const{
		Vec ans;
		ans.x=x-b.x;
		ans.y=y-b.y;
		return ans;
	}
	bool operator <(const Vec &b)const{
		return (__int128)y*b.x<(__int128)b.y*x;
	}
};
bool cmp_x(Vec a,Vec b){
	return a.x<b.x;
}
Vec make_Vec(ll x,ll y){
	Vec ans;
	ans.x=x,ans.y=y;
	return ans;
}
void ins(vector<Vec> &a,Vec t){
	int l=(int)a.size();
	if (l==0){
		a.push_back(t);
		return;
	}
	if (t.x==a[l-1].x){
		if (t.y>a[l-1].y)return;
		a.pop_back(),l--;
	}
	while(l>1&&((t-a[l-1])<(a[l-1]-a[l-2])))a.pop_back(),l--;
	a.push_back(t);
	return;
}
namespace Case1{
	vector<node> awa[200005];
	int book[200005];
	int sz[200005],sum,rt;
	void get_rt(int now,int fa){
		sz[now]=1;
		int mx=0;
		for (int i=first[now];i;i=nxt[i])
			if (v[i]!=fa&&book[v[i]]==0){
				get_rt(v[i],now);
				sz[now]+=sz[v[i]];
				mx=max(mx,sz[v[i]]);
			}
		mx=max(mx,sum-sz[now]);
		if (2*mx<=sum)rt=now;
		return;
	}
	ll depth[200005];
	vector<Vec> qwq,conv;
	vector<node> ovo;
	void dfs2(int now,int fa,ll d){
		depth[now]=d;
		qwq.push_back(make_Vec(-a[now],2*d));
		for (int i=0;i<(int)awa[now].size();i++)ovo.push_back(awa[now][i]);
		for (int i=first[now];i;i=nxt[i])
			if (v[i]!=fa&&book[v[i]]==0)dfs2(v[i],now,d+w[i]);
		return;
	}
	void dfs1(int now){
		qwq.clear(),ovo.clear();
		dfs2(now,0,0);
		sort(qwq.begin(),qwq.end(),cmp_x);
		conv.clear();
		for (int i=0;i<(int)qwq.size();i++)ins(conv,qwq[i]);
		sort(ovo.begin(),ovo.end(),cmp_c);
		int len=(int)conv.size();
		int p=0;
		for (int i=0;i<(int)ovo.size();i++){
			int id=ovo[i].id,c=ovo[i].c,l=ovo[i].l;
			while(p+1<len&&(conv[p+1]-conv[p])<make_Vec(1,c))p++;
			ans[id]=min(ans[id],2*depth[l]+conv[p].y-conv[p].x*c);
		}
		book[now]=1;
		get_rt(now,0);
		for (int i=first[now];i;i=nxt[i]){
			if (book[v[i]]==1)continue;
			sum=sz[v[i]],rt=0;
			get_rt(v[i],now);
			dfs1(rt);
		}
		return;
	}
	void work(){
		for (int i=1;i<=q;i++)awa[d[i].l].push_back(d[i]);
		dfs1(1);
		return;
	}
}
namespace Case2{
	vector<Vec> tree[524288];
	int p[524288];
	void pushup(int now){
		int pl=0,pr=0;
		while(pl<(int)tree[now*2].size()&&pr<(int)tree[now*2+1].size()){
			if (tree[now*2][pl].x<tree[now*2+1][pr].x)ins(tree[now],tree[now*2][pl]),pl++;
			else ins(tree[now],tree[now*2+1][pr]),pr++;
		}
		while(pl<(int)tree[now*2].size())ins(tree[now],tree[now*2][pl]),pl++;
		while(pr<(int)tree[now*2+1].size())ins(tree[now],tree[now*2+1][pr]),pr++;
		return;
	}
	void build(int now,int nowl,int nowr){
		tree[now].clear();
		p[now]=0;
		if (nowl==nowr){
			int id=nfd[nowl];
			tree[now].push_back(make_Vec(-a[id],2*depth[id]));
			return;
		}
		int mid=(nowl+nowr)/2;
		build(now*2,nowl,mid);
		build(now*2+1,mid+1,nowr);
		pushup(now);
		return;
	}
	ll ask(int now,int nowl,int nowr,int lt,int rt,int c){
		if (nowl>=lt&&nowr<=rt){
			while(p[now]+1<(int)tree[now].size()&&(tree[now][p[now]+1]-tree[now][p[now]])<make_Vec(1,c))p[now]++;
			return tree[now][p[now]].y-tree[now][p[now]].x*c;
		}
		int mid=(nowl+nowr)/2;
		ll s=inf;
		if (mid>=lt)s=min(s,ask(now*2,nowl,mid,lt,rt,c));
		if (mid+1<=rt)s=min(s,ask(now*2+1,mid+1,nowr,lt,rt,c));
		return s;
	}
	void work(){
		build(1,1,n);
		for (int i=1;i<=q;i++){
			int x=d[i].s;
			while(x!=0&&depth[x]>depth[d[i].l]){
				ans[d[i].id]=min(ans[d[i].id],ask(1,1,n,dfn[x],dfo[x],d[i].c)-2*depth[x]);
				x=fa[top[x]];
			}
			x=d[i].t;
			while(x!=0&&depth[x]>depth[d[i].l]){
				ans[d[i].id]=min(ans[d[i].id],ask(1,1,n,dfn[x],dfo[x],d[i].c)-2*depth[x]);
				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[d[i].id]=min(ans[d[i].id],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[d[i].id]=min(ans[d[i].id],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++){
		d[i].id=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;
	sort(d+1,d+1+q,cmp_c);
	Case1::work();
	Case2::work();
	Case3::work();
	for (int i=1;i<=q;i++)ans[d[i].id]+=depth[d[i].s]+depth[d[i].t]-2*depth[d[i].l];
	for (int i=1;i<=q;i++)write(ans[i]),putchar('\n');
	return 0;
}