#include<iostream>
#include<cstdio>
#include<vector>
#include<algorithm>
#define N 800000
#define M 30
using namespace std;
long long read()
{
	char c=0;
	long long sum=0;
	while (c<'0'||c>'9') c=getchar();
	while ('0'<=c&&c<='9') sum=sum*10+c-'0',c=getchar();
	return sum;
}
const int inf=(int)(1e9);
struct reads
{
	int num,snum;
	long long data;
};
struct points
{
	int x;
	long long y;
};
int n,m,q,maxn,leng,length,rt,SD[N+1],X[N+1],Y[N+1],L[N+1],lg[N+1],p[N+1],fa[N+1],ls[N+1],rs[N+1],a[N+1],depth[N+1],smz,sz[N+1],minn,sx,sy,sd,sw;
long long ans[N+1],dis[N+1][M+1];
vector<reads>E[N+1];
vector<reads>ES[N+1];
vector<points>v[N+1];
bool used[N+1],vis[N+1];
void add(int x,int y,int z,long long w)
{
	E[x].push_back((reads){y,z,w}),E[y].push_back((reads){x,z,w});
	return;
}
void add2(int x,int y,long long z)
{
	++leng,ES[x].push_back((reads){y,leng,z}),ES[y].push_back((reads){x,leng,z});
	return;
}
bool cmp(int x,int y)
{
	return a[x]<a[y];
}
void dfs(int x)
{
	int nw=0,d=0;
	used[x]=1;
	for (int i=0;i<E[x].size();++i)
		if (!used[E[x][i].num])
		{
			dfs(E[x][i].num);
			if (!nw) nw=E[x][i].num,d=E[x][i].data;
			else ++length,add2(length,nw,d),add2(length,E[x][i].num,E[x][i].data),nw=length,d=0;
		}
	if (nw) add2(x,nw,d);
	return;
}
void get_rt(int x)
{
	vis[x]=sz[x]=1;
	for (int i=0;i<ES[x].size();++i)
		if (!used[ES[x][i].snum]&&!vis[ES[x][i].num])
		{
			get_rt(ES[x][i].num),sz[x]+=sz[ES[x][i].num];
			if (max(sz[ES[x][i].num],smz-sz[ES[x][i].num])<minn) minn=max(sz[ES[x][i].num],smz-sz[ES[x][i].num]),sx=x,sy=ES[x][i].num,sd=ES[x][i].snum,sw=ES[x][i].data;
		}
	vis[x]=0;
	return;
}
void dfs2(int x,int d)
{
	vis[x]=1;
	for (int i=0;i<ES[x].size();++i)
		if (!used[ES[x][i].snum]&&!vis[ES[x][i].num])
			dis[ES[x][i].num][d]=dis[x][d]+ES[x][i].data,dfs2(ES[x][i].num,d);
	vis[x]=0;
	return;
}
int solve(int x,int szt,int d)
{
	maxn=max(maxn,d),smz=szt,minn=inf,get_rt(x);
	if (minn==inf)
	{
		depth[x]=d;
		return x;
	}
	int nw=++length,tx=sx,ty=sy,dx=szt-sz[sy],dy=sz[sy];
	depth[nw]=d,used[sd]=1,dfs2(sx,d),dis[sy][d]=sw,dfs2(sy,d),ls[nw]=solve(tx,dx,d+1),rs[nw]=solve(ty,dy,d+1),fa[ls[nw]]=fa[rs[nw]]=nw;
	return nw;
}
points operator + (points a,points b)
{
	return (points){a.x+b.x,a.y+b.y};
}
points operator - (points a,points b)
{
	return (points){a.x-b.x,a.y-b.y};
}
long long operator * (points a,points b)
{
	return 1ll*a.x*b.y-1ll*a.y*b.x;
}
bool check(points a,points b,points c)
{
	if (a.x==b.x&&a.x==c.x) return b.y>=min(a.y,c.y);
	return (b-a)*(c-a)<=0;
}
int lca(int x,int y)
{
	if (depth[x]<depth[y]) swap(x,y);
	while (depth[x]!=depth[y]) x=fa[x];
	while (x!=y) x=fa[x],y=fa[y];
	return x;
}
int main()
{
	int x,y,sx,tx,d1,d2,d,sd,ps,l;
	points ds;
	long long s,t,z;
	for (int i=2;i<=N;++i) lg[i]=lg[i>>1]+1;
	length=n=read(),m=read(),q=read();
	for (int i=1;i<=n;++i) a[i]=read(),p[i]=i;
	sort(p+1,p+n+1,cmp);
	for (int i=1;i<=n-1;++i) x=read(),y=read(),z=read(),add(x,y,i,z);
	dfs(1);
	for (int i=1;i<=n;++i) used[i]=0;
	rt=solve(1,length,1);
	for (int i=1;i<=q;++i) s=read(),t=read(),d1=(s-1)/n+1,d2=(t-1)/n+1,sd=SD[i]=abs(d1-d2),x=X[i]=s-(d1-1)*n,y=Y[i]=t-(d2-1)*n,l=L[i]=lca(X[i],Y[i]),ans[i]=dis[x][depth[l]]+dis[y][depth[l]]+1ll*min(a[x],a[y])*sd;
	for (int w=1;w<=maxn;++w)
	{
		for (int i=1;i<=length;++i) v[i].clear();
		for (int i=1;i<=n;++i)
		{
			sx=p[i];
			for (int j=depth[p[i]];j>=w+1;--j)
			{
				ds=(points){a[p[i]],dis[p[i]][j-1]+dis[p[i]][w]};
				while (v[sx].size()>=2&&check(v[sx][(int)(v[sx].size())-2],v[sx].back(),ds)) v[sx].pop_back();
				v[sx].push_back(ds),sx=fa[sx];
			}
		}
		for (int i=1;i<=q;++i)
		{
			x=X[i],y=Y[i],sd=SD[i],sx=l=L[i];
			for (int j=depth[l];j>=2;--j)
			{
				if (ls[fa[sx]]==sx)
				{
					d=depth[fa[sx]],tx=rs[fa[sx]];
					if (d==w&&!v[tx].empty())
					{
						ps=0;
						for (int k=lg[v[tx].size()];k>=0;--k)
							if (ps+(1<<k)<v[tx].size()&&1ll*v[tx][ps+(1<<k)].x*sd+v[tx][ps+(1<<k)].y<1ll*v[tx][ps+(1<<k)-1].x*sd+v[tx][ps+(1<<k)-1].y)
								ps+=(1<<k);
						ans[i]=min(ans[i],1ll*v[tx][ps].x*sd+v[tx][ps].y+dis[x][j-1]+dis[y][j-1]);
					}
				}
				else
				{
					d=depth[fa[sx]],tx=ls[fa[sx]];
					if (d==w&&!v[tx].empty())
					{
						ps=0;
						for (int k=lg[v[tx].size()];k>=0;--k)
							if (ps+(1<<k)<v[tx].size()&&1ll*v[tx][ps+(1<<k)].x*sd+v[tx][ps+(1<<k)].y<1ll*v[tx][ps+(1<<k)-1].x*sd+v[tx][ps+(1<<k)-1].y)
								ps+=(1<<k);
						ans[i]=min(ans[i],1ll*v[tx][ps].x*sd+v[tx][ps].y+dis[x][j-1]+dis[y][j-1]);
					}
				}
				sx=fa[sx];
			}
			sx=x;
			for (int j=depth[x];j>=depth[l]+2;--j)
			{
				if (ls[fa[sx]]==sx)
				{
					d=depth[l],tx=rs[fa[sx]];
					if (d==w&&!v[tx].empty())
					{
						ps=0;
						for (int k=lg[v[tx].size()];k>=0;--k)
							if (ps+(1<<k)<v[tx].size()&&1ll*v[tx][ps+(1<<k)].x*sd+v[tx][ps+(1<<k)].y<1ll*v[tx][ps+(1<<k)-1].x*sd+v[tx][ps+(1<<k)-1].y)
								ps+=(1<<k);
						ans[i]=min(ans[i],1ll*v[tx][ps].x*sd+v[tx][ps].y+dis[x][j-1]+dis[y][depth[l]]);
					}
				}
				else
				{
					d=depth[l],tx=ls[fa[sx]];
					if (d==w&&!v[tx].empty())
					{
						ps=0;
						for (int k=lg[v[tx].size()];k>=0;--k)
							if (ps+(1<<k)<v[tx].size()&&1ll*v[tx][ps+(1<<k)].x*sd+v[tx][ps+(1<<k)].y<1ll*v[tx][ps+(1<<k)-1].x*sd+v[tx][ps+(1<<k)-1].y)
								ps+=(1<<k);
						ans[i]=min(ans[i],1ll*v[tx][ps].x*sd+v[tx][ps].y+dis[x][j-1]+dis[y][depth[l]]);
					}
				}
				sx=fa[sx];
			}
			sx=y;
			for (int j=depth[y];j>=depth[l]+2;--j)
			{
				if (ls[fa[sx]]==sx)
				{
					d=depth[l],tx=rs[fa[sx]];
					if (d==w&&!v[tx].empty())
					{
						ps=0;
						for (int k=lg[v[tx].size()];k>=0;--k)
							if (ps+(1<<k)<v[tx].size()&&1ll*v[tx][ps+(1<<k)].x*sd+v[tx][ps+(1<<k)].y<1ll*v[tx][ps+(1<<k)-1].x*sd+v[tx][ps+(1<<k)-1].y)
								ps+=(1<<k);
						ans[i]=min(ans[i],1ll*v[tx][ps].x*sd+v[tx][ps].y+dis[x][depth[l]]+dis[y][j-1]);
					}
				}
				else
				{
					d=depth[l],tx=ls[fa[sx]];
					if (d==w&&!v[tx].empty())
					{
						ps=0;
						for (int k=lg[v[tx].size()];k>=0;--k)
							if (ps+(1<<k)<v[tx].size()&&1ll*v[tx][ps+(1<<k)].x*sd+v[tx][ps+(1<<k)].y<1ll*v[tx][ps+(1<<k)-1].x*sd+v[tx][ps+(1<<k)-1].y)
								ps+=(1<<k);
						ans[i]=min(ans[i],1ll*v[tx][ps].x*sd+v[tx][ps].y+dis[x][depth[l]]+dis[y][j-1]);
					}
				}
				sx=fa[sx];
			}
		}
	}
	for (int i=1;i<=q;++i) printf("%lld\n",ans[i]);
	return 0;
}