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#include <iostream>
#include <string>
using namespace std;
int n, k, t, mts[8003], dp[8003][8003][3];
string s;

int main() {
    std::ios_base::sync_with_stdio(false);
    std::cin.tie(NULL);
    cin >> n >> k >> t >> s;

    for (int i = 1; i <= n; i++) {
        mts[i] = mts[i - 1] + (s[i - 1] == '1' || s[i - 1] == '2' ? 1 : 0);
    }

    for (int i = 0; i <= n + 2; i++)
        for (int j = 0; j <= k + 2; j++)
            for (int st = 0; st < 3; st++)
                dp[i][j][st] = -1000000000;

    dp[1][0][0] = 0;

    for (int i = 1; i <= n; i++) {
        for (int j = 0; j <= k; j++) {
            for (int st : {0, 1, 2}) {
                int cur = dp[i][j][st];
                if (cur == -1000000000) continue;

                char c = s[i - 1];
                
                if (st == 0 || st == 2) {
                    if (c == '1') {
                        if (j < k) dp[i + 1][j + 1][st] = max(dp[i + 1][j + 1][st], cur + 1);
                    }
                    else if (c == '2') {
                        dp[i + 1][j][st] = max(dp[i + 1][j][st], cur);

                        if (j < k) dp[i + 1][j + 1][st] = max(dp[i + 1][j + 1][st], cur + 1);
                    }
                    else {
                        dp[i + 1][j][st] = max(dp[i + 1][j][st], cur + 1);
                    }

                    if (st == 0 && i + 2 * t <= n) {
                        int miss = mts[i + t - 1] - mts[i - 1];
                        if (j + miss <= k) {
                            dp[i + t][j + miss][1] = max(dp[i + t][j + miss][1], cur);
                        }
                    }
                } else if (st == 1) {
                    if (c == '1' || c == '2') {
                        dp[i + 1][j][1] = max(dp[i + 1][j][1], cur);
                        
                        if (j < k) dp[i + 1][j + 1][1] = max(dp[i + 1][j + 1][1], cur);
                    }
                    else {
                        dp[i + 1][j][1] = max(dp[i + 1][j][1], cur);
                    }

                    if (i + t <= n + 1) {
                        int miss = mts[i + t - 1] - mts[i - 1];
                        if (j + miss <= k) {
                            dp[i + t][j + miss][2] = max(dp[i + t][j + miss][2], cur);
                        }
                    }
                }
            }
        }
    }

    int ans = -1;
    for (int j = 0; j <= k; j++) {
        ans = max(ans, dp[n + 1][j][0]);
        ans = max(ans, dp[n + 1][j][2]);
    }
    cout << (ans < 0 ? -1 : ans) << endl;
}