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#include <bits/stdc++.h>
#define st first
#define nd second
using namespace std;
using ld = long double;
using ll = long long;
using ull = unsigned long long;
mt19937 rng(chrono::high_resolution_clock::now().time_since_epoch().count());
mt19937_64 rng_64(chrono::high_resolution_clock::now().time_since_epoch().count());
inline int rand(int l, int r) {return uniform_int_distribution<int>(l, r)(rng);}
inline ll rand(ll l, ll r) {return uniform_int_distribution<ll>(l, r)(rng_64);}

const int MAX = 8'000;
int dp[MAX+7][MAX+7][3];

int get(int i, int j, int k){
	if(j >= 0 && i >= 0) return dp[i][j][k];
	return INT_MIN;
}

signed main(){
	cin.tie(NULL)->sync_with_stdio(false);

	int n, k, t;
	cin >> n >> k >> t;

	string s;
	cin >> s;

	for(int j = 0; j <= k; j++){
		dp[0][j][1] = INT_MIN;
		dp[0][j][2] = INT_MIN;
	}

	int skips = 0;
	for(int i = 1; i <= n; i++){
		if(s[i-1] != '3') skips++;
		if(i-t-1 >= 0 && s[i-t-1] != '3') skips--;

		for(int j = 0; j <= k; j++){
			// Jestem w domu (0)
			if(s[i-1] == '3') dp[i][j][0] = get(i-1, j, 0) + 1;
			else if(s[i-1] == '2') dp[i][j][0] = max(get(i-1, j, 0), get(i-1, j-1, 0) + 1);
			else dp[i][j][0] = get(i-1, j-1, 0) + 1;

			// Jestem w biurze (1)
			dp[i][j][1] = max(get(i-1, j, 1), get(i-t, j-skips, 0));

			// Jestem w domu i już byłem w biurze (2)
			if(s[i-1] == '3') dp[i][j][2] = get(i-1, j, 2) + 1;
			else if(s[i-1] == '2') dp[i][j][2] = max(get(i-1, j, 2), get(i-1, j-1, 2) + 1);
			else dp[i][j][2] = get(i-1, j-1, 2) + 1;
			dp[i][j][2] = max(dp[i][j][2], get(i-t, j-skips, 1));
		}
	}

	int ans = max(dp[n][k][0], dp[n][k][2]);
	if(ans < 0) ans = -1;

	cout << ans << '\n';
}