#include <bits/stdc++.h>
using namespace std;
const int N = 1e5 + 10;
int n, k, rating[N], cnt[N];
vector<int> pos[N];
set<int> zero, valid;
string result;
void solve()
{
    cin >> n >> k;
    for (int i = 1; i <= n; i++)
        cin >> rating[i];
    cin >> result;
    result = "0" + result + "0";
    for (int i = n + 1; i >= 1; i--)
    {
        pos[rating[i]].push_back(i);
        if (result[i] == '0')
        {
            zero.insert(i);
        }
        else
        {
            int nxt = *zero.upper_bound(i);
            cnt[nxt]++;
            if (cnt[nxt] >= k)
                valid.insert(nxt);
        }
    }
    int x = 0;
    for (int i = 0; i <= 100000; i++)
    {
        for (int p : pos[i])
        {
            int nxt = *zero.upper_bound(p);
            if (result[p] == '0')
            {
                zero.erase(p);
                valid.erase(p);
                cnt[nxt] += cnt[p];
                if (cnt[nxt] >= k)
                    valid.insert(nxt);
            }
            else
            {
                cnt[nxt]--;
                if (cnt[nxt] < k)
                    valid.erase(nxt);
            }
        }
        if (valid.size())
            x = i + 1;
    }
    cout << x << endl;
}
signed main()
{
    ios::sync_with_stdio(false);
    cin.tie(0);
    cout.tie(0);
    int t = 1;
    // cin >> t;
    while (t--)
    {
        solve();
    }
}