#include<algorithm>
#include<fstream>
#include<string>

using namespace std;

ifstream in( "substr.in" );
ofstream out( "substr.out" );

const int nmax = 16384;
const int logmax = 14;

struct str{
  int ind;
  int x;
  int y;

  str() {}
  str( int _ind, int _x, int _y ) { ind = _ind, x = _x, y = _y; }

  bool operator < (const str &a) const {
    return (x != a.x) ? (x < a.x) : (y < a.y);
  }
  bool operator == (const str &a) const {
    return (x == a.x) && (y == a.y);
  }
};

int n, k;
int p[logmax + 1][nmax + 1];
string s;
str v[nmax + 1];

inline int max2( int x, int y ) {
  return (x < y ? y : x);
}

inline int val( char x ) {
  if (x >= '0' && x <= '9') {
    return x - '0';
  } else if ( x >= 'a' && x <= 'z' ) {
    return 10 + x - 'a';
  } else return 10 + 26 + x - 'A';
}

void suffix_array() {
  for (int i = 1; i <= n; ++ i) {
    p[0][i] = val(s[i - 1]);
  }

  for (int i = 1; i <= logmax; ++ i) {
    for (int j = 1; j <= n; ++ j) {
      int x = 0;
      if ( j + (1 << (i - 1)) <= n ) {
        x = p[i - 1][j + (1 << (i - 1))];
      }
        v[j] = str( j, p[i - 1][j], x );
      }
      sort(v + 1, v + n + 1);

      int nr = 1;
      for (int j = 1; j <= n;) {
        int ind = j; str aux = v[j];
        while (ind <= n && aux == v[ind]) {
          p[i][v[ ind ].ind] = nr;
          ++ind;
        }

        ++nr;
        j = ind;
      }
    }
}

int lcp( int x, int y ) {
  int ans = 0;
  for (int i = logmax; i >= 0; -- i) {
    if (x + (1 << i) - 1 <= n && y + (1 << i) - 1 <= n && p[i][x] == p[i][y]) {
      ans += (1 << i);
      x += (1 << i);
      y += (1 << i);
    }
  }
  return ans;
}

int main() {
  in >> n >> k >> s;
  suffix_array();

  int ans = 0;
  for (int i = 1; i <= n - k + 1; ++ i) {
    ans = max2(ans, lcp(v[i].ind, v[i + k - 1].ind));
  }

  out << ans << "\n";

  in.close();
  out.close();
  return 0;
}