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#include <bits/stdc++.h>

using namespace std;
using LL = long long;
#define FOR(i, l, r) for(int i = (l); i <= (r); ++i)
#define REP(i, n) FOR(i, 0, (n) - 1)
#define ssize(x) int(x.size())

template<class A, class B> auto &operator<<(ostream &o, pair<A, B> p) {
    return o << '(' << p.first << ", " << p.second << ')';
}

template<class T> auto operator<<(ostream &o, T x) -> decltype(x.end(), o) {
    o << '{'; int i = 0; for (auto e : x) o << (", ")+2*!i++ << e;
    return o << '}';
}

#ifdef DEBUG
#define debug(x...) cerr << "[" #x "]: ", [](auto... $) {((cerr << $ << "; "), ...); }(x), cerr << '\n';
#else
#define debug(...) {}
#endif


vector<int> pref1, pref2;

int all_meetings(int x, int y) {
    return pref2[y] - pref2[x - 1] + pref1[y] - pref1[x - 1];
}

int office_meetings(int x, int y) {
    return pref1[y] - pref1[x - 1];
}


int main() {
    ios_base::sync_with_stdio(false);
    cin.tie(nullptr);

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

    pref1.resize(n + 1);
    pref2.resize(n + 1);
    REP(i, n) {
        pref1[i + 1] = pref1[i];
        pref2[i + 1] = pref2[i];
        if (s[i] == '1')
            pref1[i + 1]++;
        if (s[i] == '2')
            pref2[i + 1]++;
    }

    int ans = -1;
    if (office_meetings(1, n) <= k)
        ans = n - max(0, all_meetings(1, n) - k);

    FOR(i, t, n) {
        FOR(j, i + t, n) {
            int missed_car = all_meetings(i - t + 1, i) + all_meetings(j - t + 1, j);
            int missed_home = office_meetings(1, i - t) + office_meetings(j + 1, n);
            if (missed_car + missed_home > k)
                continue;

            int all_home = all_meetings(1, i - t) + all_meetings(j + 1, n);
            ans = max(ans, i - t + n - j - max(0, all_home - (k - missed_car)));
        }
    }

    cout << ans << '\n';

    return 0;
}