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

typedef long long ll;
typedef __float128 ld;

#define pii pair<int, int>
#define fi first
#define se second
#define VI vector<int>
#define VII vector<vector<int> >

const int N = 100500;
const int inf = 1e9 + 100;
const ll infll = 2e18 + 500;

vector<int> vec[N];

int lft[N], rht[N], rt[N], val[N], A[N];
char str[N];

int find_lft(int u) {
	if (u != lft[u]) lft[u] = find_lft(lft[u]);
	return lft[u];
}
int find_rht(int u) {
	if (u != rht[u]) rht[u] = find_rht(rht[u]);
	return rht[u];
}
int find_rt(int u) {
	if (u != rt[u]) rt[u] = find_rt(rt[u]);
	return rt[u];
}

int main() {
    ios::sync_with_stdio(0);
    cin.tie(0); cout.tie(0);

    int n, m;
    cin >> n >> m;
    for (int i = 1; i <= n; i++) {
    	int a;
    	cin >> a;
    	vec[a].push_back(i);
    	A[i] = a;
    }
    cin >> str;
    for (int i = 1; i <= n; i++) {
    	lft[i] = rht[i] = rt[i] = i, val[i] = str[i - 1] - '0';
    }
    int ans = 0, cnt = 0;
    for (int i = 1; i < n; i++) {
    	if (str[i - 1] == '1' && str[i] == '1') {
    		int u = find_rt(i), v = find_rt(i + 1);
    		if (A[u] < A[v]) swap(u, v);
    		rt[v] = u;
    		if (val[u] >= m) cnt--;
    		if (val[v] >= m) cnt--;
    		val[u] += val[v];
    		if (val[u] >= m) cnt++;
    	}
    }
    for (int tt = 0; tt <= 1e5; tt++) {
    	for (auto p : vec[tt]) {
    		if (str[p - 1] == '1') {
    			int u = find_rt(p);
    			if (val[u] == m) cnt--;
    			val[u]--;
    		}
    	}
    	for (auto p : vec[tt]) {
    		if (str[p - 1] == '0') {
    			lft[p] = p - 1, rht[p] = p + 1;
    			int l = find_lft(p), r = find_rht(p);
    			if (str[l - 1] == '0' || str[r - 1] == '0') continue;
    			int u = find_rt(l), v = find_rt(r);
    			if (A[u] < A[v]) swap(u, v);
    			rt[v] = u;
	    		if (val[u] >= m) cnt--;
	    		if (val[v] >= m) cnt--;
    			val[u] += val[v];
    			if (val[u] >= m) cnt++;
    		}
    	}
    	if (cnt) ans = tt + 1;
    }
    cout << ans << '\n';

    return 0;
}