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

const int Maxn = 250500;

typedef long long LL;

struct Hashing{
    int mod, P, C;
    int Mod(int x){ return x >= mod ? x - mod : x; }
    int dMod(int x){ return x < 0 ? x + mod : x; }
    int mul(int x, int y){ return 1ll * x * y % mod; }

    int hsh[Maxn], pw[Maxn];
    void init(string st, int n, int mod_, int P_, int C_){
        mod = mod_, P = P_, C = C_;
        pw[0] = 1;
        for (int i = 1; i <= n; i++){
            hsh[i] = Mod(mul(hsh[i - 1], P) + st[i] + C);
            pw[i] = mul(pw[i - 1], P);
        }
    }
    int gethsh(int l, int r){
        if (l > r) return -P;
        int len = r - l + 1;
        int ret = dMod(hsh[r] - mul(hsh[l - 1], pw[len]));
        return ret;
    }
} Ha1, Ha2, Hb1, Hb2;

int sum[Maxn], f[Maxn];
string A, B;
int n, m, o, k;

int dif[Maxn];

namespace Match{
	const int INF = 998244353;
	const int g = 3;
	
	inline int qpow(int x, int y){
	  int ret = 1;
	  for(; y; y >>= 1){
	    if(y & 1) ret = 1ll * ret * x % INF;
	    x = 1ll * x * x % INF;
	  }
	  return ret;
	}
	
	const int SIZ = 524288;
	int W[SIZ], IW[SIZ], T[SIZ], btf[SIZ];
	
	inline void prepare(int siz){
	  int cur = qpow(g, (INF - 1) / siz);
	  W[0] = 1; for(int i = 1; i < siz; ++i) W[i] = 1ll * W[i - 1] * cur % INF;
	  cur = qpow(g, INF - 1 - (INF - 1) / siz);
	  IW[0] = 1; for(int i = 1; i < siz; ++i) IW[i] = 1ll * IW[i - 1] * cur % INF;
	  for(int i = 0; i < siz; ++i) btf[i] = (btf[i >> 1] >> 1) + (i & 1) * (siz >> 1);
	  return;
	}
	
	inline void FFT(int *vec, int siz, int IDFT){
	  for(int i = 0; i < siz; ++i) if(i < btf[i]) swap(vec[i], vec[btf[i]]);
	  for(int step = 1; step < siz; step <<= 1){
	    for(int i = 0; i < step; ++i) T[i] = ~IDFT ? W[siz / (step << 1) * i] : IW[siz / (step << 1) * i];
	    for(int i = 0; i < siz; i += step << 1){
	      int *p1 = vec + i, *p2 = vec + i + step, *p3 = T;
	      for(int j = 0; j < step; ++j, ++p1, ++p2, ++p3){
		int u = *p1, v = 1ll * (*p2) * (*p3) % INF;
		(*p1 = (u + v)) -= (*p1 >= INF ? INF : 0);
		(*p2 = (u - v)) += (*p2 < 0 ? INF : 0);
	      }
	    }
	  }
	  if(!~IDFT){
	    int coe = qpow(siz, INF - 2);
	    for(int i = 0; i < siz; ++i) vec[i] = 1ll * vec[i] * coe % INF;
	  }
	  return;
	}
	
	inline int val(char c){ return (c == '?' ? 0 : (c == 'o' ? 1 : 2)); }
		
	inline void precalc(){
		static int f[SIZ], g[SIZ], h[SIZ];
		int siz = 524288; prepare(siz);
		memset(f, 0, sizeof(f)), memset(g, 0, sizeof(g));
		for(int i = 1; i <= n; ++i)
			f[i - 1] = val(A[i]) * val(A[i]) * val(A[i]);
		for(int i = 1; i <= m; ++i)
			g[m - (i - 1)] = val(B[i]);
		FFT(f, siz, 1), FFT(g, siz, 1);
		for(int i = 0; i < siz; ++i) h[i] = (h[i] + 1ll * f[i] * g[i]) % INF;
		
		memset(f, 0, sizeof(f)), memset(g, 0, sizeof(g));
		for(int i = 1; i <= n; ++i)
			f[i - 1] = val(A[i]);
		for(int i = 1; i <= m; ++i)
			g[m - (i - 1)] = val(B[i]) * val(B[i]) * val(B[i]);
		FFT(f, siz, 1), FFT(g, siz, 1);
		for(int i = 0; i < siz; ++i) h[i] = (h[i] + 1ll * f[i] * g[i]) % INF;
		
		memset(f, 0, sizeof(f)), memset(g, 0, sizeof(g));
		for(int i = 1; i <= n; ++i)
			f[i - 1] = (INF - 2ll) * val(A[i]) * val(A[i]) % INF;
		for(int i = 1; i <= m; ++i)
			g[m - (i - 1)] = val(B[i]) * val(B[i]);
		FFT(f, siz, 1), FFT(g, siz, 1);
		for(int i = 0; i < siz; ++i) h[i] = (h[i] + 1ll * f[i] * g[i]) % INF;
		
		FFT(h, siz, -1);
		for(int i = 0; i < siz; ++i) if(i - m >= 0 && i - m < n)
			dif[i - m + 1] = h[i] / 2;
			
		// for(int i = 1; i <= n; ++i) printf("%d ", dif[i]); puts("");
	}
	
}

int calc(int p){
	return dif[p];
}

int calcval(int r){
    int l = r - m + 1;
    int cnt = calc(l);
    if (cnt >= 32)
        return 0;
    int s = sum[r] - sum[l - 1];
    return (LL) s >> cnt;
}

int main(){
    cin >> o >> k;
    cin >> A >> B, n = A.length(), m = B.length();
    A = '*' + A, B = '&' + B;

	Match::precalc();

    for (int i = 1; i <= n; i++)
        sum[i] = sum[i - 1] + (A[i] == 'o' ? o : k);
    for (int i = 1; i <= n; i++){
        f[i] = f[i - 1];
        if (i >= m) 
            f[i] = max(f[i], calcval(i) + f[i - m]);
    }
    cout << f[n] << endl;
    return 0;
}