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#include <iostream>
#include <climits>
#define OFFICE 1
#define REMOTE 2
#define FREE 3


using namespace std;

int countActivity(int* day, int n, int activity);
void runAlgorithm(int* day, int n, int leaves, int t);
void initNegative(int* arr, int n);
int initMissed(int* day, int start, int n, int activity);
void printTab(string name, int* tab, int n);
pair<int, int> findShortestRange(int* a,int* b,int n, int leaves, int t);

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

    int n, leaves, t;

    cin >> n >> leaves >> t;

    int* day = new int[n];
    
    string in;
    cin >> in;

    for (int i = 0; i < n; i++) {
        day[i] = in[i] - '0';
    }


    int offices = countActivity(day, n, OFFICE);
    int meetings = offices + countActivity(day, n, REMOTE);

    if (meetings <= leaves) {
        cout << n;
        delete[] day;
        return 0;
    }
    else if (offices <= leaves) {
        int hours = n - min(meetings, leaves);
        cout << hours;
        delete[] day;
        return 0;
    }
    else {
        runAlgorithm(day, n, leaves, t);
        delete[] day;
    }
}

int countActivity(int* day, int n, int activity) {
    int count = 0;
    for (int i = 0; i < n; i++) {
        if (day[i] == activity) count++;
    }
    return count;
}

void initNegative(int* arr, int n) {
    for (int i = 0; i < n; i++) {
        arr[i] = INT_MAX;
    }
}

int initMissed(int* day, int start, int n, int activity) {
    return countActivity(day + start, n, activity);
}

void printTab(string name, int* tab, int n) {
    cout << "\n " << name << "\n";
    for (int i = 0; i < n; i++) cout << tab[i] << " ";
    cout << "\n";
}

void runAlgorithm(int* day, int n, int leaves, int t) {
    int* a = new int[n];
    int* b = new int[n];
    initNegative(a, n);
    initNegative(b, n);

    // count missed meetings (office + possibly remotely)
    int missedOffice = initMissed(day, 0, t, OFFICE);
    int missedRemote = initMissed(day, 0, t, REMOTE);
    a[0] = missedOffice + missedRemote;

    for (int i = 1; i < n - 2 * t; i++) {
        if (day[i - 1] == REMOTE) missedRemote--;
        if (day[i + t - 1] == REMOTE) missedRemote++;
        if (day[i + t - 1] == OFFICE) missedOffice++;
        a[i] = missedOffice + missedRemote;
    }
    
    // count missed meetings (office + possibly remotely)
    missedOffice = initMissed(day, n-t, t, OFFICE);
    missedRemote = initMissed(day, n-t, t, REMOTE);
    b[n - t] = missedOffice + missedRemote;
    for (int i = n - t - 1; i > t; i--) {
        if (day[i + t] == REMOTE) missedRemote--;
        if (day[i] == REMOTE) missedRemote++;
        if (day[i] == OFFICE) missedOffice++;
        b[i] = missedOffice + missedRemote;
    }

    
    pair<int, int> startEnd = findShortestRange(a, b, n, leaves, t);

    if (startEnd.first == -1'000'000) {
        cout << -1;
        delete[] a;
        delete[] b;
        return;
    }
    else {
        int missed = a[startEnd.first] + b[startEnd.second];
        int remoteBefore = countActivity(day, startEnd.first, REMOTE);
        int remoteAfter = countActivity(day + startEnd.second + t, n - startEnd.second - t, REMOTE);
        int remoteOutside = remoteBefore + remoteAfter;
        int missedLeft = leaves - missed;

        int outdoor = (startEnd.second - startEnd.first + t);

        int worked = n - outdoor - remoteOutside + missedLeft;

        cout << worked;
    }

    delete[] a;
    delete[] b;
}

pair<int, int> findShortestRange(int* a, int* b, int n, int leaves, int t) {
    int start = -1'000'000;
    int end = 0;
    for (int i = 0; i < n; i++) {
        if (start != -1'000'000 && a[i-1] < a[i]) continue;
        for (int j = i + t + 1; j <= n - t; j++) {
            int cost = a[i] + b[j];
            if (cost <= leaves && j - i <= end - start) {
                start = i;
                end = j;
                break;
            }
        }
    }
    return { start, end };
}