#include <fstream>
#include <string>
#include <vector>

using namespace std;

ifstream fin("substr.in");
ofstream fout("substr.out");

const int sigma= 26+26+10;
const int mod1= 666013;
const int mod2= 99997;

int n, k;
int cnt[mod1];

string s;

struct str {
     int x, y;
};

vector <str> v[mod1];

inline str mp( int x, int y ) {
     str sol;
     sol.x= x, sol.y= y;

     return sol;
}

int value( char x ) {
     if ( x>='0' && x<='9' ) {
          return x-'0';
     } else if ( x>='a' && x<='z' ) {
          return 10+x-'a';
     }
     return 10+26+x-'A';
}

bool check( int x ) {
     int p1= 1, p2= 1;
     for ( int i= 1; i<=x-1; ++i, p1= (p1*sigma)%mod1, p2= (p2*sigma)%mod2 ) ;

     int h1= 0, h2= 0;
     for ( int i= 1; i<=x; ++i ) {
          h1= (h1*sigma+value(s[i-1]))%mod1;
          h2= (h2*sigma+value(s[i-1]))%mod2;
     }
     cnt[h1]= x;
     v[h1].clear();
     v[h1].push_back(mp(h2, 1));

     if ( 1>=k ) {
          return 1;
     }

     for ( int i= x+1; i<=n; ++i ) {
          h1= (((h1-p1*value(s[i-1-x]))*sigma+value(s[i-1]))%mod1+mod1)%mod1;
          h2= (((h2-p2*value(s[i-1-x]))*sigma+value(s[i-1]))%mod2+mod2)%mod2;
          if ( cnt[h1]!=x ) {
               v[h1].clear();
               cnt[h1]= x;
          }

          int ok= 0;
          for ( int j= 0; j<(int)v[h1].size() && ok==0; ++j ) {
               if ( v[h1][j].x==h2 ) {
                    ++v[h1][j].y;
                    ok= 1;

                    if ( v[h1][j].y>=k ) {
                         return 1;
                    }
               }
          }
          if ( ok==0 ) {
               v[h1].push_back(mp(h2, 1));
          }
     }

     return 0;
}

int main(  ) {
     fin>>n>>k>>s;

     int sol= 0, step;
     for ( step= 1; step*2<=n; step*= 2 ) ;
     for ( ; step>0; step/= 2 ) {
          if ( sol+step<=n && check(sol+step) ) {
               sol+= step;
          }
     }

     fout<<sol<<"\n";

     return 0;
}