#include <cstdio>

 #include <cstring>

 #include <algorithm>

 using namespace std;

 const int maxn =  + ;

 const int maxm =  + ;

 int s[maxn];

 int sa[maxn], height[maxn], rank[maxn];

 int t[maxn], t2[maxn], c[maxm];

 int n, k;

 void build_sa(int m)

 {

     int i, *x = t, *y = t2;

     for(i = ; i < m; i++) c[i] = ;

     for(i = ; i < n; i++) c[x[i] = s[i]]++;

     for(i = ; i < m; i++) c[i] += c[i - ];

     for(i = n - ; i >= ; i--) sa[--c[x[i]]] = i;

     for(int k = ; k <= n; k <<= )

     {

         int p = ;

         for(i = n - k; i < n; i++) y[p++] = i;

         for(i = ; i < n; i++) if(sa[i] >= k) y[p++] = sa[i] - k;

         for(i = ; i < m; i++) c[i] = ;

         for(i = ; i < n; i++) c[x[y[i]]]++;

         for(i = ; i < m; i++) c[i] += c[i - ];

         for(i = n - ; i >= ; i--) sa[--c[x[y[i]]]] = y[i];

         swap(x, y);

         p = ; x[sa[]] = ;

         for(i = ; i < n; i++)

             x[sa[i]] = y[sa[i]]==y[sa[i-]] && y[sa[i]+k]==y[sa[i-]+k] ? p -  : p++;

         if(p >= n) break;

         m = p;

     }

 }

 void build_height()

 {

     int i, j, k = ;

     for(i = ; i < n; i++) rank[sa[i]] = i;

     for(i = ; i < n; i++)

     {

         if(k) k--;

         j = sa[rank[i] - ];

         while(s[i + k] == s[j + k]) k++;

         height[rank[i]] = k;

     }

 }

 bool ok(int len)

 {

     int cnt = ;

     for(int i = ; i < n; i++)

     {

         if(i ==  || height[i] < len) cnt = ;

         if(++cnt >= k) return true;

     }

     return false;

 }

 int main()

 {

     //freopen("in.txt", "r", stdin);

     scanf("%d%d", &n, &k);

     for(int i = ; i < n; i++)

     {

         scanf("%d", &s[i]);

         s[i]++;

     }

     s[n] = ;

     build_sa();

     build_height();

     int L = , R = n;

     while(L < R)

     {

         int M = (L + R + ) / ;

         if(ok(M)) L = M;

         else R = M - ;

     }

     printf("%d\n", L);

     return ;

 }