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

#define dbg(x...) \
do { \
std::cout << #x << " -> "; \
err(x); \
} while (0)

void err() {
	std::cout << std::endl;
}

template<class T, class... Ts>
void err(T arg, Ts &... args) {
	std::cout << fixed << setprecision(10) << arg << ' ';
	err(args...);
}

const int maxn = 1e5 + 5;
int a[maxn];
string res;
vector<int>p[maxn];
struct SegTree {
#define ls(p) p << 1
#define rs(p) p << 1 | 1
	int L[maxn << 2],R[maxn << 2],V[maxn << 2],Siz[maxn << 2];
	
	inline void Push_up(int i) {
		if (L[ls(i)] == Siz[ls(i)]) L[i] = L[ls(i)] + L[rs(i)];
		else L[i] = L[ls(i)];
		if (R[rs(i)] == Siz[rs(i)]) R[i] = R[rs(i)] + R[ls(i)];
		else R[i] = R[rs(i)];
		Siz[i] = Siz[ls(i)] + Siz[rs(i)];
		V[i] = max({L[i],R[i],R[ls(i)] + L[rs(i)]});
	}
	
	void Build (int p,int l,int r) {
		if (l == r) {
			//dbg(l,Id[l]);
			Siz[p] = 1;
			V[p] = L[p] = R[p] = res[l - 1] - '0'; 
			return;
		}
		int mid = (l + r) >> 1;
		Build(ls(p),l,mid);
		Build(rs(p),mid + 1,r);
		Push_up(p);
	}
	
	void Update(int p,int l,int r,int x) {
		if (l == r) {
			L[p] = R[p] = Siz[p] = V[p] = 0;
			return;
		}
		int mid = (l + r) >> 1;
		if (x <= mid) Update(ls(p),l,mid,x);
		else Update(rs(p),mid + 1,r,x);
		Push_up(p);
	}
} Tr;


void GENSHEN_START() {
	int n,k;cin >> n >> k;
	for (int i = 1;i <= n;i++) {
		cin >> a[i];
		p[a[i]].push_back(i);
	}
	cin >> res;
	Tr.Build(1,1,n);
	int ans = 0;
	if (Tr.V[1] >= k) ans = 1;
	for (int i = 1;i <= 1e5;i++) {
		for (auto j : p[i]) {
			Tr.Update(1,1,n,j);
		}
		if (Tr.V[1] >= k) ans = i + 1;
	}
	cout << ans << '\n';
	return ;
}

signed main()
{
	ios::sync_with_stdio(false);cin.tie(nullptr);
	int T = 1;
	//cin >> T;
	while (T--) GENSHEN_START();
	return 0;
}