#include <bits/stdc++.h>
#define maxN 16386
#define maxL 16
using namespace std;
int ans, n, k, l, cnt, P[maxL][maxN], nr, pos[maxN];
char s[maxN];
struct entry
{
    int nr[2], p;
} V[maxN];
bool cmp(const entry &a, const entry &b)
{
    return (a.nr[0] == b.nr[0]) ? (a.nr[1] < b.nr[1]) : (a.nr[0] < b.nr[0]);
}
void read()
{
    freopen("substr.in", "r", stdin);
    scanf("%d %d\n", &n, &k);
    scanf("%s", s);
}
void prec()
{
    int k, i, cnt = 1;
    for (i = 0; i < n; ++ i)
        P[0][i] = s[i] - 'a';
    for (k = 1; cnt < 2 * n; ++ k, cnt <<= 1)
    {
        for (i = 0; i < n; ++ i)
        {
            V[i].nr[0] = P[k - 1][i];
            V[i].nr[1] = i + cnt < n ? P[k - 1][i + cnt] : -1;
            V[i].p = i;
        }
        sort(V, V + n, cmp);
        nr = 0;
        for (i = 0; i < n; ++ i)
            if (i > 0 && V[i].nr[0] == V[i - 1].nr[0] && V[i].nr[1] == V[i - 1].nr[1])
            {
                P[k][V[i].p] = P[k][V[i - 1].p];
                pos[++ nr] = V[i].p;
            }
            else
            {
                P[k][V[i].p] = i;
                pos[++ nr] = V[i].p;
            }
        l = k;
    }
}

int lcp(int x, int y)
{
    int k, ans = 0;
    if (x == y) return n - x;
    for (k = l; k >= 0 && x < n && y < n; -- k)
        if (P[k][x] == P[k][y])
        {
            x += (1 << k);
            y += (1 << k);
            ans += (1 << k);
        }
    return ans;
}
void solve()
{
    int i, x, y, z;
    prec();
    for (i = 0; i <= n - k; ++ i)
    {
        x = pos[i];
        y = pos[i + k - 1];
        z = lcp(x, y);
        if (z > ans)
            ans = z;
    }
}
void write()
{
    freopen("substr.out", "w", stdout);
    printf("%d\n", ans);
}
int main()
{
    read();
    solve();
    write();
    return 0;
}