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#include <bits/stdc++.h>

using namespace std;

typedef unsigned uint;
typedef long long ll;
typedef unsigned long long ull;
typedef long double ldbl;
typedef pair<int, int> pii;
typedef pair<uint, uint> puu;
typedef pair<ll, ll> pll;
typedef pair<ull, ull> pull;
typedef pair<double, double> pdd;
typedef vector<int> vi;
typedef vector<uint> vu;
typedef vector<ll> vll;
typedef vector<ull> vull;
typedef vector<pii> vpii;
typedef vector<puu> vpuu;
typedef vector<pll> vpll;
typedef vector<pull> vpull;
typedef vector<string> vstr;
typedef vector<double> vdbl;
typedef vector<ldbl> vldbl;
#define pb push_back
#define ppb pop_back
#define pfr push_front
#define ppfr pop_front
#define emp emplace
#define empb emplace_back
#define be begin
#define rbe rbegin
#define all(x) (x).be(), (x).end()
#define rall(x) (x).rbe(), (x).rend()
#define fir first
#define sec second
#define mkp make_pair
#define brif(cond) if (cond) break
#define ctif(cond) if (cond) continue
#define retif(cond) if (cond) return
void fastio() {ios_base::sync_with_stdio(false);cin.tie(nullptr);}
template<typename T> T gcd(T a, T b) {return b ? gcd(b, a%b) : a;}
template<typename T> T extgcd(T a, T b, T &x, T &y)
{
    T x0 = 1, y0 = 0, x1 = 0, y1 = 1;
    while (b) {
        T q = a/b; a %= b; swap(a, b);
        x0 -= q*x1; swap(x0, x1);
        y0 -= q*y1; swap(y0, y1);
    }
    x = x0; y = y0; return a;
}
int ctz(uint x) {return __builtin_ctz(x);}
int ctzll(ull x) {return __builtin_ctzll(x);}
int clz(uint x) {return __builtin_clz(x);}
int clzll(ull x) {return __builtin_clzll(x);}
int popcnt(uint x) {return __builtin_popcount(x);}
int popcntll(ull x) {return __builtin_popcountll(x);}
int bsr(uint x) {return 31^clz(x);}
int bsrll(ull x) {return 63^clzll(x);}

template<typename T>
void umax(T &dst, T src) { dst = max(dst, src); }

#define N 8016

char a[N];
int pre[N];
int dp[N][N][3];

int main()
{
    fastio();

    int n, k, t;
    int ans = -1;

    cin >> n >> k >> t >> a;
    for (int i = 0; i < n; ++i) pre[i+1] = pre[i]+(a[i]<'3');
    for (int i = 0; i <= n; ++i) {
        for (int j = 0; j <= k; ++j) {
            for (int w : {0, 1, 2}) dp[i][j][w] = -1;
        }
    }
    dp[0][0][0] = 0;
    for (int i = 0; i < n; ++i) {
        for (int j = 0; j <= k; ++j) {
            for (int w : {0, 1, 2}) {
                ctif(dp[i][j][w] < 0);
                /// meeting:
                if (a[i] == '2' || (a[i] == '1' && w == 1)) umax(dp[i+1][j][w], dp[i][j][w]);
                /// solve/work/nothing:
                umax(dp[i+1][j+pre[i+1]-pre[i]][w], dp[i][j][w]+(w!=1));
                /// drive:
                if (w < 2 && i+t <= n) umax(dp[i+t][j+pre[i+t]-pre[i]][w+1], dp[i][j][w]);
            }
        }
    }
    /*cerr << "DP:\ni\\j"; for (int j = 0; j <= k; ++j) cerr << '\t' << j; cerr << '\n';
    for (int i = 0; i <= n; ++i) {
        cerr << i;
        for (int j = 0; j <= k; ++j) {
            cerr << '\t';
            for (int w : {0, 1, 2}) {
                if (w) cerr << ',';
                if (dp[i][j][w] < 0) cerr << '_';
                else cerr << dp[i][j][w];
            }
        }
        cerr << '\n';
    }*/
    for (int j = 0; j <= k; ++j) {
        for (int w : {0, 2}) umax(ans, dp[n][j][w]);
    }
    cout << ans << '\n';

    return 0;
}