#include <fstream>
#include <unordered_map>
 
using namespace std;
 
ifstream cin("substr.in");
ofstream cout("substr.out");
 
const int mod = int(1e9) + 7;
const int mod_ = 666013;
int N, K;
string str;
int h[16385], h_[16385];
int INV[16385], INV_[16385];
unordered_map<int,int> H, H_;
 
inline int getIndex(char x) {
   return x - 'a' + 1;
}
 
int logpow(int a,int b,const int &m) {
    int ret = 1;  
    for (;b > 0;b >>= 1, a = 1LL * a * a % m) {
        if (b & 1) {
            ret = 1LL * ret * a % m;
        }
    }
    return ret;
}

void compute() {
    int X = 26;
    int X_ = 26;
    h[1] = getIndex(str[0]);
    h_[1] = getIndex(str[0]);
    INV[0] = 1;
    INV_[0] = 1;
    for (int i = 2;i <= N;i++,X = 1LL * X * 26 % mod, X_ = 1LL * X_ * 26 % mod_) {
        h[i] = (1LL * h[i - 1] + 1LL * X * getIndex(str[i - 1])) % mod;
        h_[i] = (1LL * h_[i - 1] + 1LL * X_ * getIndex(str[i - 1])) % mod_;
    	INV[i - 1] = logpow(X,mod - 2,mod);
        INV_[i - 1] = logpow(X_,mod_ - 2,mod_);
    }
}

inline int getHash(int l,int r) {
    return 1LL * (h[r] - h[l - 1] + mod) * INV[l - 1] % mod;
}

inline int getHash_(int l,int r) {
    return 1LL * (h_[r] - h_[l - 1] + mod_) * INV_[l - 1] % mod_;
}
 
bool isGood(int L) {
    int hash, hash_;
    H.clear();
    H_.clear();
    for (int i = 1;i + L - 1 <= N;i++) {
        hash = getHash(i,i + L - 1);
        hash_ = getHash_(i,i + L - 1);
        H[hash]++;
        H_[hash_]++;        
        if(H[hash] >= K && H_[hash_] >= K) {
             return true;
        }
    }
    return false;
}
 
int main()
{
    cin >> N >> K;
    cin.get();
    getline(cin,str);
    compute();
    int ans = 0;
    for (int step = 1 << 15;step > 0;step >>= 1) {
        if(step + ans <= N && isGood(step + ans)) {
            ans += step;  
        }
    }
    cout << ans;
    return 0; 
}