#include <bits/stdc++.h>


using namespace std;

template<typename T_container, typename T = typename enable_if<!is_same<T_container, string>::value, typename T_container::value_type>::type> ostream& operator<<(ostream &os, const T_container &v) { os << '{'; string sep; for (const T &x : v) os << sep << x, sep = ", "; return os << '}'; }
 void dbg_out() { cerr << endl; }
template<typename Head, typename... Tail> void dbg_out(Head H, Tail... T) { cerr << ' ' << H; dbg_out(T...); }
#ifdef ONPC
  #define deb(...) cerr << '[' <<  __LINE__ << "] (" << #__VA_ARGS__ << "):", dbg_out(__VA_ARGS__)
#else
  #pragma GCC optimize("O3,unroll-loops")
  #pragma GCC target("avx2,bmi,bmi2,lzcnt,popcnt")
  #define deb(...)
#endif

// c++ short types
#define vt vector
//typedef long long ll;
typedef long double ld;

void whattime() { cout << "finished in " << clock() * 1.0 / CLOCKS_PER_SEC << " sec" << endl; }
// const int mod = 1e9 + 7;
const int mod = 998244353;
const int inf = 1e9;
const int64_t infll = 1e13;
bool debug = false;
const ld eps = 1e-9;
const ld pi = acos(-1);
mt19937_64 rng((int) chrono::steady_clock::now().time_since_epoch().count());

const int max_K = 31;

bool equal(char a, char b) {
	return a == '?' || b == '?' || a == b;
}


vt<vt<int>> pfun(const string &s, int a) {
	vt<vt<int>> p(s.size(), vt<int>(max_K, 0));
	for(int i = a; i < (int)s.size(); ++i) {
		for(int j = 0; j < max_K; ++j) {
			int g = p[i-1][j];
			while(g && !equal(s[i], s[g])) g = p[g-1][j];
			p[i][j] = g + equal(s[i], s[g]);
		}
		for(int j = 0; j + 1 < max_K; ++j) {
			p[i][j+1] = max(p[i][j+1], p[i-1][j] + 1);
		}
	}
	return p;
}

void solve() {
	int o, k;
	cin >> o >> k;
	string s, p;
	cin >> s >> p;
	auto pi = pfun(p + "#" + s, p.size()+1);
	vt<int> what(s.size(), max_K);
	for(int i = p.size() + 1; i < s.size() + p.size() + 1; ++i) {
		for(int j = 0; j < max_K; ++j) if(pi[i][j] >= p.size()) {
			what[i - p.size() - 1] = j;
			break;
		}
	}
	int cost = 0;
 	vt<int> dp(s.size(), 0), vertices(40, 0);
	for(int i = 0; i < int(s.size()); ++i) {
		if(i) {
			dp[i] = dp[i-1];
		}
		if(i >= p.size()) {
			if(s[i - p.size()] == 'o') {
				cost -= o;
			} else {
				cost -= k;
			}
		}
		if(s[i] == 'o') {
			cost += o;
		} else {
			cost += k;
		}
		if(i + 1 >= p.size()) {
			int value = cost >> what[i];
			if(i >= p.size()) {
				value += dp[i-p.size()];
			}
			dp[i] = max(dp[i], value);
		}
	}
	cout << dp.back() << '\n';
}


int main()
{
	// ios::sync_with_stdio(false); cin.tie(nullptr);
#ifdef ONPC
	freopen("C:\\Users\\raf4i\\CLionProjects\\cp\\inp.txt", "r", stdin);
#endif
	int tt = 1;
	if(debug) {
		tt = 1e6;
	} else {
    // cin >> tt;
	}
	for(int t = 0; t < tt; ++t) {
		solve();
	}

#ifdef ONPC
	whattime();
#endif

	return 0;
}