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

#define FOR(i, a, b) for(int i = (a); i < (b); i++)
#define RFOR(i, a, b) for(int i = (a) - 1; i >= (b); i--)
#define SZ(a) int(a.size())
#define ALL(a) a.begin(), a.end()
#define PB push_back
#define MP make_pair
#define F first
#define S second

typedef long long LL;
typedef vector<int> VI;
typedef vector<LL> VL;
typedef pair<int, int> PII;
typedef pair<LL, LL> PLL;
typedef double db;

const int mod = 998244353;
const int N = 1e4;

int add(int a, int b)
{
	return a + b < mod ? a + b : a + b - mod;
}

int sub(int a, int b)
{
	return a - b >= 0 ? a - b : a - b + mod;
}

int mult(int a, int b)
{
	return (LL)a * b % mod;
}

int binpow(int a, LL n)
{
	int res = 1;
	while (n)
	{
		if (n & 1)
			res = mult(res, a);
		a = mult(a, a);
		n /= 2;
	}
	return res;
}

template<typename T>
void updMin(T& a, T b)
{
	a = min(a, b);
}

template<typename T>
void updMax(T& a, T b)
{
	a = max(a, b);
}

int cnt[N][4];

int main()
{
	ios::sync_with_stdio(0); 
	cin.tie(0);
	int n, k, t;
	string s;
	cin >> n >> k >> t >> s;
	FOR(i, 0, n)
	{
		FOR(j, 1, 4)
		{
			cnt[i + 1][j] = cnt[i][j];
		}
		cnt[i + 1][s[i] - '0']++;
	}
	int ans = -1;
	if (cnt[n][1] <= k)
	{
		ans = cnt[n][3] + min(cnt[n][1] + cnt[n][2], k);
	}
	FOR(i, 0, n - 2 * t + 1)
	{
		FOR(j, i + t, n - t + 1)
		{
			int m1 = cnt[i + t][1] + cnt[n][1] - cnt[j][1];
			int m2 = cnt[i + t][2] - cnt[i][2] + cnt[j + t][2] - cnt[j][2];
			if (m1 + m2 <= k)
			{
				int c1 = cnt[i][1] + cnt[n][1] - cnt[j + t][1];
				int c2 = cnt[i][2] + cnt[n][2] - cnt[j + t][2];
				int c3 = cnt[i][3] + cnt[n][3] - cnt[j + t][3];
				updMax(ans, c3 + c1 + min(c2, k - (m1 + m2)));
			}
		}
	}
	cout << ans << "\n";
	return 0;
}