#include <cstdio>

#define nm 20010
#define b 79
#define mod 1555571

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

int n, k, a[nm], h[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 + b * b) * 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] = 0;
    }
    
    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] = 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;

    	++h[aux];

        if (rez < h[aux])
        	rez = h[aux];
    }

    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;
}