#include <stdio.h>
#include <vector>
#include <algorithm>

#define nm 20010
#define b 79
#define mod 555557

using namespace std;

int max(int);
int egal(int, int, int);

int n, k, a[nm];
vector <int> h[mod], nr[mod];

int main()
{
	int i, crt, step;
    char ch;

	freopen("substr.in", "r", stdin);
    freopen("substr.out", "w", stdout);

    scanf("%d%d", &n, &k);

    for (i = 1; i <= n; ++i)
    {
    	scanf(" %c ", &ch);
    	a[i] = ((ch + 200) * 123) % mod;
    }

    for (step = 1; step < n; step <<= 1);

    for (crt = 0; step; step >>= 1)
    {
    	if (crt + step <= n && max(crt + step) >= k)
        	crt += step;
            
    	for (i = 0; i < mod; ++i)
        {
        	h[i].clear();
            nr[i].clear();
        }
    }
    
    printf("%d\n", crt);

	return 0;
}

int max(int l)
{
	int i, j, aux, pow, rez = 1;

    for (aux = 0, i = 1; i <= l; ++i)
    	aux = (aux * b + a[i]) % mod;

    h[aux].push_back(1);
    nr[aux].push_back(1);

    for (pow = i = 1; i < l; ++i)
    	pow = (pow * b) % mod;

    for (i = l + 1; i <= n; ++i)
    {
    	aux = aux - ((long long)((long long)a[i - l] * pow) % mod);

        if (aux < 0)
        	aux += mod;

        aux = (aux * b + a[i]) % mod;

        for (j = 0; j < h[aux].size(); ++j)
        	if (egal(h[aux][j], i - l + 1, l))
            {
            	++nr[aux][j];

                if (rez < nr[aux][j])
                	rez = nr[aux][j];
                    
                break;
            }

    	if (j == h[aux].size())
        {
        	h[aux].push_back(i - l + 1);
            nr[aux].push_back(1);
        }
    }

    return rez;
}

int egal(int s1, int s2, int l)
{
	int i;

    for (i = 0; i < l; ++i)
    	if (a[s1 + i] != a[s2 + i])
        	return 0;

    return 1;
}