#include<cstdio>
#include<cstring>
#include<algorithm>
using namespace std;
char s[16385];
int a[15][16385];
struct pereche
{
    char c;
    int poz;
};

bool cmp(pereche a,pereche b)
{
    return a.c<b.c;
}

pereche v[16385];

struct perint
{
    int x,y,poz;
};

bool cmpi(perint a,perint b)
{
    if(a.x==b.x)
        return a.y<b.y;
    return a.x<b.x;
}

int detput(int x)
{
    int nr=1;
    while(nr<=x)
    {
        nr*=2;
    }
    nr/=2;
    return nr;
}

int putd(int x)
{
    int nr=0;
    while(x)
    {
        nr++;
        x/=2;
    }
    return nr;
}

perint vv[16385];
int main()
{
    freopen("substr.in","r",stdin);
    freopen("substr.out","w",stdout);
    int n,k,i,nr,j,st,dr,med,nrp,ok;
    scanf("%d%d\n%s",&n,&k,s);
    for(i=0;i<n;++i)
    {
        v[i].c=s[i];
        v[i].poz=i;
    }
    sort(v,v+n,cmp);
    nr=0;
    for(i=0;i<n;++i)
    {
        if(i&&v[i].c!=v[i-1].c)
            nr++;
        a[0][v[i].poz]=nr;
    }
    for(i=2,nrp=1;i<=n;i*=2,++nrp)
    {
        for(j=0;j<n;++j)
        {
            vv[j].x=a[nrp-1][j];
            if(j+i/2>=n)
                vv[j].y=-1;
            else
                vv[j].y=a[nrp-1][j+(i/2)];
            vv[j].poz=j;
        }
        sort(vv,vv+n,cmpi);
        nr=0;
        for(j=0;j<n;++j)
        {
            if(j&&(vv[j].x!=vv[j-1].x||vv[j].y!=vv[j-1].y))
                nr++;
            a[nrp][vv[j].poz]=nr;
        }
    }
    st=1;
    dr=n;
    int sol=1;
    for(i=0;i<nrp;++i)
    {
        sort(a[i],a[i]+n);
    }
    while(st<=dr)
    {
        med=(st+dr)/2;
        ok=0;
        for(j=0;j<n-med;++j)
        {
            int val=med,lp=j;
            while(val)
            {
                int vald=detput(val);
                int pd=putd(vald);
                if(a[pd][lp]==a[pd][lp+med-1])
                {
                    val-=vald;
                    lp+=vald;
                }
                else
                    break;
            }
            if(!val)
            {
                ok=1;
                break;
            }
        }
        if(ok)
        {
            sol=med;
            st=med+1;
        }
        else
            dr=med-1;
    }
    printf("%d\n",sol);
    return 0;
}