#include <bits/stdc++.h>

#pragma GCC optimize("O3")
//#define int long long

using namespace std;

#define rep(i, a, b) for(int i = a; i < (b); ++i)
#define all(x) begin(x), end(x)
#define sz(x) (int)(x).size()
typedef long long ll;
typedef pair<int, int> pii;
typedef vector<int> vi;

signed main(){
	cin.tie(0);
	ios::sync_with_stdio(0);
	int k, n, M = 1000000007;
	cin >> k >> n;
	vector<int> h(26);
	for(int &x : h) cin >> x;
	string a, b;
	cin >> a >> b;
	vector<vector<int>> dp(k,vector<int>(n));
	for(int i = k-1; i >= 0; i--){
		for(int j = n-1; j >= 0; j--){
			dp[i][j] = (j < n-1? dp[i][j+1] : 0);
			if(a[i] == b[j]){
				if(i < k-1 && j+h[a[i]-'A']+1 < n) dp[i][j] += dp[i+1][j+h[a[i]-'A']+1];
				if(i == k-1) dp[i][j]++;
				if(dp[i][j] >= M) dp[i][j] -= M;
			}
		}
	}
	cout << dp[0][0] << "\n";
}