#include <bits/stdc++.h>
using namespace std;

void debug(const char *msg, ...) {
#ifdef CLESIP
    va_list arg;
    static char pbString[512];
    va_start(arg,msg);
    vsprintf(pbString,msg,arg);
    cerr << "[DEBUG] " << pbString << "\n";
    va_end(arg);
#endif    
}

using u64 = unsigned long long;
using i64 = long long;
using i128 = __int128_t;
template <typename T, typename L> void chkmax(T &x, L y) { if (x < y) x = y; }
template <typename T, typename L> void chkmin(T &x, L y) { if (x > y) x = y; }

const int N = 2e5 + 10;
const int W = 26;
const int K = 70;
const i64 INF = 1e18;
const u64 B = 131;
int n, m, a[N], apr[2][W], b[K], cur, id[N], nms[N], nxt[N];
bool must[W + 1];
i64 f[N][K], sum[N];
u64 pw[N * 2], hsh[N];
char s[N], t[N], subs[N];

void calc_hash() {
	for (int i = 1; i <= cur; i ++) {
		hsh[i] = hsh[i - 1] + pw[i] * (subs[i] - 'a' + 77);
	}
}

u64 get_hash(int l, int r) {
	return (hsh[r] - hsh[l - 1]) * pw[cur - l];
}

void solve() {
	cin >> n >> m >> (s + 1) >> (t + 1);
	for (int i = 1; i <= n; i ++)
		cin >> a[i];
	for (int i = 0; i < W; i ++)
		apr[0][i] = apr[1][i] = 0;
	for (int i = 1; i <= m; i ++) {
		if (!apr[0][t[i] - 'a'])
			apr[0][t[i] - 'a'] = i;
		apr[1][t[i] - 'a'] = i;
	}
	int cnt = 0;
	for (int i = 0; i < W; i ++) if (apr[0][i])
		b[++ cnt] = apr[0][i], b[++ cnt] = apr[1][i];
	b[++ cnt] = 1, b[++ cnt] = m + 1;
	sort(b + 1, b + 1 + cnt);
	cnt = unique(b + 1, b + 1 + cnt) - b - 1;
	for (int i = 0; i <= n; i ++)
		for (int j = 0; j <= cnt; j ++)
			f[i][j] = INF;
	f[0][0] = 0;
	s[0] = 'a' + 1;
	for (int j = 0; j < cnt; j ++) {
		int l = b[j], r = b[j + 1] - 1, len = r - l;
		// debug("current range (%d, %d)", l, r);
		for (int i = 0; i < W; i ++)
			must[i] = (apr[0][i] <= l && l < apr[1][i]);
		
		if (j > 0) {
			cur = 0;
			for (int i = 1; i <= n; i ++) {
				sum[i] = sum[i - 1];
				if (must[s[i] - 'a']) {
					subs[++ cur] = s[i];
					id[cur] = i;
				} else {
					sum[i] += a[i];
				}
			}
			nms[n + 1] = n + 1, nxt[n + 1] = n + 1;
			for (int i = n; i >= 0; i --) {
				nms[i] = nms[i + 1], nxt[i] = nxt[i + 1];
				if (must[s[i] - 'a'])
					nms[i] = i;
				if (s[i] == t[l])
					nxt[i] = i;
			}
			calc_hash();
			u64 self = 0;
			for (int i = l + 1; i <= r; i ++)
				self += pw[cur + i - l - 1] * (t[i] - 'a' + 77);
			for (int i = 0, pos = 1; i < n; i ++) if (nms[i + 1] >= nxt[i + 1] && nxt[i + 1] <= n) {
				// debug("???? i: %d j: %d f: %lld", i, j, f[i][j - 1]);
				int nxt_trans = nxt[i + 1];
				if (len > 0) {
					while (pos <= cur && id[pos] <= nxt_trans)
						++ pos;
					if (pos + len - 1 > cur || get_hash(pos, pos + len - 1) != self)
						continue;
					nxt_trans = id[pos + len - 1];
				}
				// debug("nxt_trans: %d", nxt_trans);
				chkmin(f[nxt_trans][j], f[i][j - 1] + sum[nxt_trans] - sum[i] - (!must[t[l] - 'a'] ? a[nxt[i + 1]] : 0));
				// debug("f[nxt_trans]: %lld", f[nxt_trans][j]);
			}
		}

		for (int i = 1; i <= n; i ++) if (!must[s[i] - 'a']) {
			chkmin(f[i][j], f[i - 1][j] + a[i]);
			// debug("???? f[%d][%d] = %lld", i, j, f[i][j]);
		}
	}

	if (f[n][cnt - 1] == INF)
		cout << "-1\n";
	else
		cout << f[n][cnt - 1] << "\n";
}

int main() {

	ios::sync_with_stdio(false), cin.tie(0), cout.tie(0);
	pw[0] = 1;
	for (int i = 1; i < N * 2; i ++)
		pw[i] = pw[i - 1] * B;
	solve();
	return 0;
}