// Ivan Carvalho

// Solution to https://www.spoj.com/problems/ADASEQEN/

#include <bits/stdc++.h>

using namespace std;

const int MAXN = 2e3 + 10;

int dp[MAXN][MAXN];

int v1[MAXN], v2[MAXN];

int val[MAXN];

int n, m;

char s1[MAXN], s2[MAXN];

int solve(int a, int b) {

if (!a || !b) {

return 0;

}

if (dp[a][b] != -1) return dp[a][b];

int ret = 0;

if (v1[a] == v2[b]) ret = val[v1[a]] + solve(a - 1, b - 1);

return dp[a][b] = max(ret, max(solve(a, b - 1), solve(a - 1, b)));

}

int main() {

scanf("%d %d", &n, &m);

memset(dp, -1, sizeof(dp));

for (int i = 0; i < 26; i++) {

scanf("%d", &val[i]);

}

scanf("%s", s1);

scanf("%s", s2);

for (int i = 1; i <= n; i++) {

v1[i] = s1[i - 1] - 'a';

}

for (int i = 1; i <= m; i++) {

v2[i] = s2[i - 1] - 'a';

}

printf("%d\n", solve(n, m));

return 0;

}