#include <cstdio>
#include <vector>

#define NMAX 16385
#define MOD1 733331
#define MOD2 600011
#define PRIM1 33
#define PRIM2 127

using namespace std;

typedef unsigned int ui;

char S[NMAX];
ui n, k;
vector <ui> hashTable1, hashTable2;

ui power(ui x, ui n)
{
    if(n == 0)
        return 1;
    if(n == 1)
        return x;

    ui tmpPow = power(x, n >> 1);

    if(n & 1)
        return tmpPow * tmpPow * x;
    return tmpPow * tmpPow;
}

bool okHash(ui q)
{
    hashTable1 = vector <ui> (MOD1, 0);
    hashTable2 = vector <ui> (MOD2, 0);
    ui i, P1 = power(PRIM1, q - 1), P2 = power(PRIM2, q - 1), hashQ1 = 0, hashQ2 = 0 , tmpCalc;

    for(i=0; i<q && i<n; ++i){
        hashQ1 = ((hashQ1 << 5) + hashQ1) + S[i];
        hashQ2 = ((hashQ2 << 7) - hashQ2) + S[i];
    }
    ++hashTable1[hashQ1 % MOD1];
    ++hashTable2[hashQ2 % MOD2];

    for(i=q; i<n; ++i){
        tmpCalc = hashQ1 - (S[i - q] * P1);
        hashQ1 = ((tmpCalc << 5) + tmpCalc) + S[i];

        tmpCalc = hashQ2 - (S[i - q] * P2);
        hashQ2 = ((tmpCalc << 7) - tmpCalc) + S[i];

        ++hashTable1[hashQ1 % MOD1];
        ++hashTable2[hashQ2 % MOD2];
        if(hashTable1[hashQ1 % MOD1] == hashTable2[hashQ2 % MOD2] && hashTable1[hashQ1 % MOD1] >= k)
            return true;
    }
    return false;
}

ui cautaBinDim(ui st, ui dr)
{
    ui dim = 0;
    while(st <= dr){
        ui mij = (st + dr) >> 1;

        if(okHash(mij)){
            dim = mij;
            st  = mij + 1;
        }
        else dr = mij - 1;
    }
    return dim;
}

int main()
{
    ui dim = 1;
    freopen("substr.in","r",stdin);
    freopen("substr.out","w",stdout);

    scanf("%u %u\n%s", &n, &k, S);

    dim = cautaBinDim(0, n-1);
    printf("%u\n", dim);
    return 0;
}