#include <cstdio>
#include <vector>

#define NMAX 16385
#define MOD 733331
#define PRIM 33

using namespace std;

typedef unsigned int ui;

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

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)
{
    hashTable = vector <ui> (MOD, 0);
    ui i, P = power(PRIM, q - 1), hashQ = 0, tmpCalc;

    for(i=0; i<q; ++i)
        hashQ = ((hashQ << 5) + hashQ) + (S[i] - '`');
    ++hashTable[hashQ % MOD];

    for(i=q; i<n; ++i){
        tmpCalc = hashQ - ((S[i - q] - '`') * P);
        hashQ = ((tmpCalc << 5) + tmpCalc) + (S[i] - '`');
        //printf("%u\n", hashQ);
        ++hashTable[hashQ % MOD];
        if(hashTable[hashQ % MOD] >= 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 i, dim = 0;
    freopen("substr.in","r",stdin);
    freopen("substr.out","w",stdout);

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

    for(i=n - 1; i>1; --i)
        if(okHash(i)){
            printf("%u\n", i);
            return 0;
        }

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