#include <iostream>
#include <vector>
#include <set>
using namespace std;

int main()
{
    int n, k;
    cin >> n >> k;
    vector<int> v(n);

    for(int i = 0; i < n; i++) {
        cin >> v[i];
    }
    multiset<int> ms;
    for(int i = 0; i < k; i++) {
        ms.insert(0);
    }
    vector<int> cnt(k, 0);
    int i = 0, j = 0;
    int result = 0;
    while(j < n) {
        if(*ms.begin() <= 3 and *ms.rbegin() <= 3) {
            if(v[j] < k) {
                ms.erase(ms.find(cnt[v[j]]));
                cnt[v[j]]++;
                ms.insert(cnt[v[j]]);
            }
            j++;
            if(*ms.begin() == 3 and *ms.rbegin() == 3) {
                result = max(result, j - i);
            }
        }
        else {
            if(v[i] < k) {
                ms.erase(ms.find(cnt[v[i]]));
                cnt[v[i]]--;
                ms.insert(cnt[v[i]]);
            }
            i++;
            if(*ms.begin() == 3 and *ms.rbegin() == 3) {
                result = max(result, j - i);
            }
        }
    }
    cout << result << endl;

    return 0;
}