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#include <bits/stdc++.h>

typedef bool bool_t;
typedef char char_t;
typedef long long int_t;
typedef std::string str_t;
typedef std::vector<bool_t> vecbool_t;
typedef std::vector<int_t> vecint_t;
typedef std::vector<vecint_t> vecvecint_t;
typedef std::vector<vecvecint_t> vecvecvecint_t;

int_t n, k, t;
str_t s;


void s2();

int32_t main()
{
    std::ios_base::sync_with_stdio(0);
    std::cin.tie(0);

    std::cin >> n >> k >> t >> s;

    s2();

    return 0;
}

void s2()
{
    int_t answer;
    vecint_t meetings_on_prefix(n + 1, 0);
    vecvecvecint_t dp(n + 1, vecvecint_t(k + 1, vecint_t(2, LLONG_MIN)));

    for(int_t i = 0; i < n; i++)
        meetings_on_prefix[i + 1] = meetings_on_prefix[i] + (s[i] == '1' || s[i] == '2');

    for(int_t i = 0; i <= k; i++)
        dp[0][i][0] = 0;

    for(int_t i = 1; i <= n; i++)
    {
        for(int_t j = 0; j <= k; j++)
        {
            int_t p = 0;

            if((i - t) >= 0)
                p = meetings_on_prefix[i] - meetings_on_prefix[i - t];

            if(s[i - 1] == '1')
            {
                if(j - 1 >= 0)
                    dp[i][j][0] = std::max(dp[i][j][0], dp[i - 1][j - 1][0] + 1);

                if(i - t >= 0 && j - p >= 0)
                    dp[i][j][0] = std::max(dp[i][j][0], dp[i - t][j - p][1]);

                dp[i][j][1] = std::max(dp[i][j][1], dp[i - 1][j][1]);

                if(i - t >= 0 && j - p >= 0)
                    dp[i][j][1] = std::max(dp[i][j][1], dp[i - t][j - p][0]);
            }

            if(s[i - 1] == '2')
            {
                dp[i][j][0] = std::max(dp[i][j][0], dp[i - 1][j][0]);

                if(j - 1 >= 0)
                    dp[i][j][0] = std::max(dp[i][j][0], dp[i - 1][j - 1][0] + 1);

                if(i - t >= 0 && j - p >= 0)
                    dp[i][j][0] = std::max(dp[i][j][0], dp[i - t][j - p][1]);

                dp[i][j][1] = std::max(dp[i][j][1], dp[i - 1][j][1]);

                if(i - t >= 0 && j - p >= 0)
                    dp[i][j][1] = std::max(dp[i][j][1], dp[i - t][j - p][0]);
            }

            if(s[i - 1] == '3')
            {
                dp[i][j][0] = std::max(dp[i][j][0], dp[i - 1][j][0] + 1);

                if(i - t >= 0 && j - p >= 0)
                    dp[i][j][0] = std::max(dp[i][j][0], dp[i - t][j - p][1]);

                dp[i][j][1] = std::max(dp[i][j][1], dp[i - 1][j][1]);

                if(i - t >= 0 && j - p >= 0)
                    dp[i][j][1] = std::max(dp[i][j][1], dp[i - t][j - p][0]);
            }
        }
    }

    answer = dp[n][k][0];

    if(answer < 0)
        answer = -1;

    std::cout << answer << '\n';
}