#define _USE_MATH_DEFINES
#include <bits/stdc++.h>
using namespace std;
#define FOR(i,m,n) for(int i=(m);i<(n);++i)
#define REP(i,n) FOR(i,0,n)
#define ALL(v) (v).begin(),(v).end()
using ll = long long;
constexpr int INF = 0x3f3f3f3f;
constexpr long long LINF = 0x3f3f3f3f3f3f3f3fLL;
constexpr double EPS = 1e-8;
constexpr int MOD = 1000000007;
// constexpr int MOD = 998244353;
constexpr int dy[] = {1, 0, -1, 0}, dx[] = {0, -1, 0, 1};
constexpr int dy8[] = {1, 1, 0, -1, -1, -1, 0, 1}, dx8[] = {0, -1, -1, -1, 0, 1, 1, 1};
template <typename T, typename U> inline bool chmax(T &a, U b) { return a < b ? (a = b, true) : false; }
template <typename T, typename U> inline bool chmin(T &a, U b) { return a > b ? (a = b, true) : false; }
struct IOSetup {
  IOSetup() {
    std::cin.tie(nullptr);
    std::ios_base::sync_with_stdio(false);
    std::cout << fixed << setprecision(20);
  }
} iosetup;

int main() {
  int n, k; string s; cin >> n >> k >> s;
  vector<bool> dp(n + 1, true);
  int w = 1, l = 0;
  for (int i = n - 1; i >= 0; --i) {
    dp[i] = (i > 0 && s[i - 1] == 'x') || l > 0;
    ++(dp[i] ? w : l);
    if (i + k <= n) --(dp[i + k] ? w : l);
  }
  // REP(i, n + 1) cout << dp[i];
  if (!dp[0]) {
    cout << "0\n";
    return 0;
  }
  vector<int> ans;
  FOR(i, 1, k + 1) {
    if (!dp[i]) ans.emplace_back(i);
  }
  assert(ans.size() == 1);
  cout << ans[0] << '\n';
  return 0;
}