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

#define REP(i,a,b) for(int i=(a),i##_end_=(b);i<i##_end_;++i)

static const int M=250003;
int o,k,Fa[M];
char S[M],P[M];
int Nxt[M],n,m;
int Sum[M],Val[M];
int GetFa(int x){return Fa[x]==x?x:Fa[x]=GetFa(Fa[x]);}
vector<int>QO,QK;
int F[M];

int main(){
  scanf("%d%d",&o,&k);
  scanf("%s%s",S+1,P);
  n=strlen(S+1);int op=n+1,kp=n+1;
  m=strlen(P);
  REP(i,1,n+1)
    if(S[i]=='o')QO.push_back(i);
    else QK.push_back(i);
  
  for(int i=n;i>=1;--i){
    if(S[i]=='o')Nxt[i]=op,op=i;
    else Nxt[i]=kp,kp=i;
  }
  REP(i,1,n+1){
    Sum[i]=Sum[i-1]+(S[i]=='o'?o:k);
    Fa[i]=i;
  }
  REP(i,1,n-m+2)
    Val[i]=Sum[i+m-1]-Sum[i-1];
  
  //REP(i,1,n-m+2)cout<<Sum[i]<<' ';cout<<endl;

  REP(i,0,strlen(P)){
    if(P[i]=='?')continue;
    int p;
    if(P[i]=='k'){
      p=lower_bound(QO.begin(),QO.end(),i+1)-QO.begin();
      int pe=QO.size();
      while(p<pe){
        if(QO[p]-i>n-m+1)break;
        if(!(Val[QO[p]-i]>>=1))
          Fa[QO[p]-i-1]=QO[p]-i;
        p=max(p+1,(int)(lower_bound(QO.begin(),QO.end(),GetFa(QO[p]-i)+i+1)-QO.begin()));
      }
    }
    else{
      p=lower_bound(QK.begin(),QK.end(),i+1)-QK.begin();
      int pe=QK.size();
      while(p<pe){
        if(QK[p]-i>n-m+1)break;
        if(!(Val[QK[p]-i]>>=1))
          Fa[QK[p]-i-1]=QK[p]-i;
        p=max(p+1,(int)(lower_bound(QK.begin(),QK.end(),GetFa(QK[p]-i)+i+1)-QK.begin()));
      }
    }
  }
  REP(i,1,n+2){
    F[i]=max(F[i],F[i-1]);
    if(i<=n-m+1)
      F[i+m]=max(F[i+m],F[i]+Val[i]);
  }
  printf("%d\n",F[n+1]);
  return 0;
}