#include<iostream>
#include<cstdio>
#include<algorithm>
#include<cstring>
#include<bitset>
#define N 250003
#define ll long long
using namespace std;
bitset<N> bt,tp,pr,ppr;
char s[N],p[N];
ll dp[N];
int o,k,n,m;
ll qpow(ll x,int b){
ll ans=1;
b=min(b,60);
return (1ll<<b);
}
ll sum[N];
int main(){
  scanf("%d%d",&o,&k);
  scanf("%s",s+1);
  n=strlen(s+1);
  scanf("%s",p+1);
  int m=strlen(p+1);
  bt.reset();
  tp.reset();
  pr.reset();
  ppr.reset();
  for(int i=1;i<=m;i++)tp.set(i);
  for(int i=1;i<=m;i++){
    if(p[i]!='?')ppr.set(i);
  }
  for(int i=1;i<=m;i++){
    if(p[i]=='k')pr.set(m-i+1);
  }
  for(int i=1;i<=n;i++){
    if(s[i]=='k')sum[i]=sum[i-1]+k;
    else sum[i]=sum[i-1]+o;
  }
  dp[0]=0;
  for(int i=1;i<=n;i++){
    bt<<=1;
    if(s[i]=='k')bt.set(1);
    bt&=tp;
    ll kk=((bt^pr)&ppr).count();
    // cout<<"err:"<<i<<" "<<kk<<endl;
    dp[i]=dp[i-1];
    if(i>=m)dp[i]=max(dp[i],dp[i-m]+(sum[i]-sum[i-m])/qpow(2,kk));
    // cout<<"dp:"<<i<<" "<<dp[i]<<" "<<(sum[i]-sum[i-m])<<" "<<(sum[i]-sum[i-m])/qpow(2,kk)<<endl;
  }
  printf("%lld\n",dp[n]);
 
}