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

int main() {
    int n, k, t;
    cin >> n >> k >> t;
    string s;
    cin >> s;
    vector<int> czyn(n);
    for (int i = 0; i < n; ++i) {
        czyn[i] = s[i] - '0';
    }

    vector<int> prefix(n + 1, 0);
    for (int i = 0; i < n; ++i) {
        prefix[i + 1] = prefix[i] + ((czyn[i] == 1 || czyn[i] == 2) ? 1 : 0);
    }

    vector<vector<int>> dpdom(k + 1, vector<int>(n + 1, -1));
    vector<vector<int>> dpbi(k + 1, vector<int>(n + 1, -1));
    dpdom[0][0] = 0;

    for (int j = 0; j < n; ++j) {
        for (int i = 0; i <= k; ++i) {
            if (dpdom[i][j] != -1) {
                int current = dpdom[i][j];
                int cat = czyn[j];
                if (cat == 1) {
                    if (i < k) {
                        dpdom[i + 1][j + 1] = max(dpdom[i + 1][j + 1], current);
                    }
                } else if (cat == 2) {
                    dpdom[i][j + 1] = max(dpdom[i][j + 1], current);
                    if (i < k) {
                        dpdom[i + 1][j + 1] = max(dpdom[i + 1][j + 1], current + 1);
                    }
                } else {
                    dpdom[i][j + 1] = max(dpdom[i][j + 1], current + 1);
                }

                if (j + t <= n) {
                    int a = j;
                    int b = j + t;
                    int sum_miss = prefix[b] - prefix[a];
                    if (i + sum_miss <= k) {
                        int ni = i + sum_miss;
                        dpbi[ni][b] = max(dpbi[ni][b], current);
                    }
                }
            }

            if (dpbi[i][j] != -1) {
                int current = dpbi[i][j];
                int cat = czyn[j];
                dpbi[i][j + 1] = max(dpbi[i][j + 1], current);

                if (j + t <= n) {
                    int a = j;
                    int b = j + t;
                    int sum_miss = prefix[b] - prefix[a];
                    if (i + sum_miss <= k) {
                        int ni = i + sum_miss;
                        dpdom[ni][b] = max(dpdom[ni][b], current);
                    }
                }
            }
        }
    }

    int result = -1;
    for (int i = 0; i <= k; ++i) {
        result = max(result, dpdom[i][n]);
        result = max(result, dpbi[i][n]);
    }
    cout << (result == -1 ? -1 : result) << endl;

    return 0;
}