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#include <bits/stdc++.h>

using std::cin, std::cout;
using i32 = int;
using u32 = unsigned int;
using i64 = long long;
using u64 = unsigned long long;
const char endl = '\n';

const int MAX_N = 8005;

enum state {
    BEFORE = 0,
    WORK = 1,
    AFTER = 2,
};

enum task {
    WORK_MEET = 0,
    MEET = 1,
    NONE = 2,
};

int best[3][MAX_N][MAX_N];

int main() {
    std::ios_base::sync_with_stdio(0);
    cin.tie(NULL);
    cout.tie(NULL);

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

    std::string s;
    cin >> s;

    int total_jobs = 0;

    const int START_SCORE = 10000;

    best[state::BEFORE][0][0] = START_SCORE;

    for (int i = 0; i < s.size(); i++) {
        task type = (task)(s[i] - '1');
        if (type == MEET or type == WORK_MEET) total_jobs++;

        // AFTER -> AFTER
        for (int jobs_done = 0; jobs_done <= n; jobs_done++) {
            int curr_score = best[state::AFTER][i][jobs_done];

            if (curr_score + 1 > best[state::AFTER][i + 1][jobs_done]) best[state::AFTER][i + 1][jobs_done] = curr_score + 1;
            if (type == MEET) {
                if (curr_score > best[state::AFTER][i + 1][jobs_done + 1]) best[state::AFTER][i + 1][jobs_done + 1] = curr_score;
            }
        }

        // WORK -> WORK / AFTER
        for (int jobs_done = 0; jobs_done <= n; jobs_done++) {
            int curr_score = best[state::WORK][i][jobs_done];

            if (i <= n - t) {
                if (curr_score > best[state::AFTER][i + t][jobs_done]) best[state::AFTER][i + t][jobs_done] = curr_score;
            }

            if (curr_score > best[state::WORK][i + 1][jobs_done]) best[state::WORK][i + 1][jobs_done] = curr_score;
            if (type == MEET or type == WORK_MEET) {
                if (curr_score > best[state::WORK][i + 1][jobs_done + 1]) best[state::WORK][i + 1][jobs_done + 1] = curr_score;
            }
        }

        // BEFORE -> BEFORE / WORK
        for (int jobs_done = 0; jobs_done <= n; jobs_done++) {
            int curr_score = best[state::BEFORE][i][jobs_done];

            if (i <= n - t) {
                if (curr_score > best[state::WORK][i + t][jobs_done]) best[state::WORK][i + t][jobs_done] = curr_score;
            }

            if (curr_score + 1 > best[state::BEFORE][i + 1][jobs_done]) best[state::BEFORE][i + 1][jobs_done] = curr_score + 1;
            if (type == MEET) {
                if (curr_score > best[state::BEFORE][i + 1][jobs_done + 1]) best[state::BEFORE][i + 1][jobs_done + 1] = curr_score;
            }
        }
    }

    int max = 0;
    for (int jobs_done = std::max(0, total_jobs - k); jobs_done <= total_jobs; jobs_done++) {
        int score = std::max(best[state::AFTER][n][jobs_done], best[state::BEFORE][n][jobs_done]);
        if (score > max) max = score;
    }
    if (max < START_SCORE) cout << -1;
    else cout << max - START_SCORE;

    return 0;
}