#include <cstdio>
#include <algorithm>
#define DIMN 17000
using namespace std;
int f[300],sff_arr[15][3*DIMN],w[DIMN];
char s[DIMN];
struct ceva{
    int x,y,poz;
};
ceva v[DIMN];
int n;
int cmp (ceva a,ceva b){
    if (a.x!=b.x)
        return a.x<=b.x;
    else return a.y<=b.y;
}
int lcp (int p2,int a,int b){ /// cel mai lung prefix dintre cel care inc pe a si pe b
    int sol=0,i;
    for (i=p2;i>=0 && a<=n && b<=n; i--){
        if (sff_arr[i][a]==sff_arr[i][b]){
            sol+=(1<<i);
            a+=(1<<i);
            b+=(1<<i);
        }
    }
    return sol;
}
int main()
{
    FILE *fin=fopen ("substr.in","r");
    FILE *fout=fopen ("substr.out","w");
    int k,i,elem,dif,j,pmax,maxi;
    fscanf (fin,"%d%d\n",&n,&k);
    fgets (s+1,20000,fin);

    for (i=0;i<10;i++)
        f[i+'0']=i+1;
    for (i='A';i<='Z';i++)
        f[i]=10+i-'A';
    for (i='a';i<='z';i++)
        f[i]=10+'Z'-'A'+i-'a';

    for (i=1;i<=n;i++)
        sff_arr[0][i]=f[s[i]]; /// nr de ordine al suff de l (1<<0) care inc pe i

    for (i=1;(1<<i)<=n;i++){
        for (j=1;j<=n;j++){
            v[j].x=sff_arr[i-1][j];
            v[j].y=sff_arr[i-1][j+(1<<(i-1))];
            v[j].poz=j;
        }
        sort (v+1,v+n+1,cmp);
        dif=0;
        for (j=1;j<=n;j++){
            if (v[j].x!=v[j-1].x || v[j].y!=v[j-1].y)
                dif++;
            sff_arr[i][v[j].poz]=dif;
            w[sff_arr[i][v[j].poz]]=v[j].poz;
        }
    }
    /// w e ala sortat crescator
    pmax=i-2;
    maxi=0;
    for (i=1;i+k-1<=n;i++){
        //if (i==15989)
          //  printf ("%d ",maxi);
        maxi=max(maxi,lcp(pmax,w[i],w[i+k-1]));
    }
    fprintf (fout,"%d",maxi);
    return 0;
}