#include<bits/stdc++.h>
#define ll long long
#define endl '\n'
#define up(i,j,k,l) for(int i=j;i<=k;i+=l)
#define down(i,j,k,l) for(int i=j;i>=k;i-=l)
using namespace std;
const int N=2e1+10;
int n,k;
int a[N][N];
int s,t;
int ut,vt;
void solve()
{	
	cin>>n>>k;
	char u,v;
	int w;
	up(i,0,N-1,1){
		up(j,0,N-1,1){
			a[i][j]=INT_MAX;
		}
	}
	up(i,1,n-1,1){
		cin>>w;
		a[i][i+1]=w;
		a[i+1][i]=w;
	}
	cin>>w;
	a[1][n]=w;
	a[n][1]=w;
	up(i,1,k,1){
		cin>>u>>v>>w;
		ut=u-'A'+1;
		vt=v-'A'+1;
		if(a[ut][vt]==INT_MAX){
			a[ut][vt]=w;
			a[vt][ut]=w;
		}
		else{
			a[ut][vt]=max(a[ut][vt],w);
			a[vt][ut]=max(a[vt][ut],w);
		}
	}
	cin>>u>>v;
	s=u-'A'+1;
	t=v-'A'+1;
	up(l,1,n,1){
		up(i,1,n,1){
			up(j,1,n,1){
				a[i][j]=min(a[i][j],a[i][l]+a[l][j]);
			}
		}
	}
	cout<<a[s][t];
	return;
}
int main()
{
    //ios::sync_with_stdio(false);
	//cin.tie(0);
	//freopen(".in","r",stdin);
	//freopen(".out","w",stdout);
	int _=1;
	//cin>>_;
	up(i,1,_,1){
		solve();
	}
	return 0;
}