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// Hallelujah, praise the one who set me free
// Hallelujah, death has lost its grip on me
// You have broken every chain, There's salvation in your name
// Jesus Christ, my living hope
#include <bits/stdc++.h>
using namespace std;

#define REP(i, s, e) for (int i = (s); i < (e); i++)
#define RREP(i, s, e) for (int i = (s); i >= (e); i--)
template <class T> inline bool mnto(T &a, T b) { return b < a ? a = b, 1 : 0; }
template <class T> inline bool mxto(T &a, T b) { return a < b ? a = b, 1 : 0; }

typedef unsigned long long ull;
typedef long long ll;
typedef long double ld;
#define FI first
#define SE second
typedef pair<int, int> ii;
typedef pair<ll, ll> pll;
typedef tuple<int, int, int> iii;
#define ALL(_a) _a.begin(), _a.end()
#define SZ(_a) (int)_a.size()
#define pb push_back
typedef vector<int> vi;
typedef vector<ll> vll;
typedef vector<ii> vii;
typedef vector<iii> viii;

#ifndef DEBUG
#define cerr                                                                   \
  if (0)                                                                       \
  cerr
#endif

const int INF = 1000000005;
const ll LINF = 1000000000000000005ll;
const int MAXN = 8005;

int n, k, t;
string s;
int a[MAXN];
int psm[MAXN];
int dp[MAXN][MAXN][2];

int main() {
#ifndef DEBUG
  ios::sync_with_stdio(0), cin.tie(0);
#endif
  cin >> n >> k >> t;
  cin >> s;
  REP(i, 0, n) { a[i + 1] = s[i] - '0'; }
  REP(i, 1, n + 1) { psm[i] = psm[i - 1] + (a[i] != 3); }
  REP(j, 0, k + 1) {
    REP(b, 0, 2) { dp[0][j][b] = -INF; }
  }
  dp[0][0][0] = 0;
  REP(i, 1, n + 1) {
    REP(j, 0, k + 1) {
      REP(b, 0, 2) { dp[i][j][b] = -INF; }
    }
    REP(j, 0, k + 1) {
      if (a[i] == 1) {
        if (j) {
          mxto(dp[i][j][0], dp[i - 1][j - 1][0] + 1);
        }
        mxto(dp[i][j][1], dp[i - 1][j][1]);
      } else if (a[i] == 2) {
        if (j) {
          mxto(dp[i][j][0], dp[i - 1][j - 1][0] + 1);
        }
        mxto(dp[i][j][0], dp[i - 1][j][0]);
        mxto(dp[i][j][1], dp[i - 1][j][1]);
      } else {
        mxto(dp[i][j][0], dp[i - 1][j][0] + 1);
        mxto(dp[i][j][1], dp[i - 1][j][1]);
      }
      if (i >= t) {
        int delta = psm[i] - psm[i - t];
        if (j >= delta) {
          REP(b, 0, 2) { mxto(dp[i][j][b], dp[i - t][j - delta][b ^ 1]); }
        }
      }
    }
  }
  int ans = -INF;
  REP(j, 0, k + 1) { mxto(ans, dp[n][j][0]); }
  if (ans < 0) {
    cout << -1 << '\n';
  } else {
    cout << ans << '\n';
  }
  return 0;
}