#include<bits/stdc++.h>

using namespace std;

#define Rabbir_Reaper ios_base::sync_with_stdio(0); cin.tie(0);

#define int long long

const int N = 2e5 + 5;

string c;

unordered_map<char,pair<int,int>> ump;

priority_queue<pair<int,int>,vector<pair<int,int>>,greater<pair<int,int>>> pq;

int sum,ans=0;

signed main(){

    Rabbir_Reaper

    int n,m;

    cin>>n>>m;

    cin>>c;

    cin>>ump['W'].first;

    cin>>ump['M'].first;

    cin>>ump['L'].first;

    cin>>ump['W'].second;

    cin>>ump['M'].second;

    cin>>ump['L'].second;

    for(int i=0;i<n;i++){

        sum += ump[c[i]].first;

        while(!pq.empty() && pq.top().first < i){

            sum -= ump[c[pq.top().second]].first;

            pq.pop();

        }

        if(sum > m) ans++;

        pq.push({i+ump[c[i]].second-1,i});

    }

    cout<<ans;

}