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#include<cstdio>
#include<iostream>
#include<algorithm>
#include<string>
#include<vector>
#include<cmath>
#include<queue>
#include<queue>
#include<stack>
#include<bits/stdc++.h>
#include<ext/pb_ds/assoc_container.hpp>
#include<ext/pb_ds/tree_policy.hpp>

using namespace std;
using namespace __gnu_pbds;

typedef vector<int> VI;
typedef vector<VI> VVI;
typedef long long LL;
typedef unsigned long long ULL;
typedef long double LD;
typedef pair<int, int> PII;
typedef pair<LL, LL> PLL;
typedef vector<LL> VLL;
typedef vector<LD> VLD;
typedef vector<VLL > VVLL;
typedef vector<VLD > VVLD;
typedef vector<PII > VPII;
typedef __int128 int128;
template<class TIn>
using indexed_set = tree<
        TIn, null_type, less<TIn>,
        rb_tree_tag, tree_order_statistics_node_update>;
template<class T> using min_heap = priority_queue<T, vector<T>, greater<T>>;

#define FOR(x, b, e) for(int x=b; x<=(e); ++x)
#define FORD(x, b, e) for(int x=b; x>=(e); --x)
#define REP(x, n) for(int x=0; x<(n); ++x)
#define VAR(v, n) __typeof(n) v = (n)
#define ALL(c) (c).begin(), (c).end()
#define SIZE(x) ((int)(x).size())
#define FOREACH(i, c) for(VAR(i, (c).begin()); i != (c).end(); ++i)
#define PB push_back
#define ST first
#define ND second
#define THIS (*this)
#define LSB(x) (x & -x)
#define SQR(x) ((x)*(x))

struct PrefSum {
    VI a;
    PrefSum(string &s, char c): a(s.size() + 1) { REP(i, s.size()) a[i + 1] = a[i] + (s[i] == c ? 1 : 0); }
    int sum(int i, int j) { return a[j + 1] - a[i]; }
};

int main() {
	ios_base::sync_with_stdio(0);
    cin.tie(NULL); cout.tie(NULL);
    int n, k, t; cin >> n >> k >> t;
    string s; cin >> s;
    PrefSum mof(s, '1'), mrem(s, '2');
    if (mof.sum(0, n - 1) <= k) {
        cout << n - max(0, mof.sum(0, n - 1) + mrem.sum(0, n - 1) - k) << '\n';
        return 0;
    }
    int ans = -1;
    for (int i = t; i < n - t && mof.sum(0, i - 1) <= k; i++) {
        int ska = mof.sum(0, i - 1) + mrem.sum(i - t, i - 1);
        int lim = i - t + n - t - 1;
        if (ska <= k) for (int j = i; j < n - t && lim - j > ans; j++) {
            int skb = mof.sum(j + 1, n - 1) + mrem.sum(j + 1, j + t);
            if (ska + skb <= k) {
                ans = max(ans, lim - j - max(0, mrem.sum(0, i - t - 1) + mrem.sum(j + t + 1, n - 1) - (k - ska - skb)));
                break;
            }
        }
    }
    cout << ans << '\n';

    return 0;
}