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

int main()
{
    int n;
    cin >> n;
    vector<int> v(n);
    
    for(int i = 0; i < n; i++) {
        cin >> v[i];
    }
    int i = 0, j = 0;
    int cnt = 0;
    int result = 0;
    while(j < n) {
        if(cnt <= 3) {
            if(v[j] == 3) {
                cnt++;
            }
            j++;
            if(cnt == 3) {
                result = max(result, j - i);
            }
        }
        else {
            if(v[i] == 3) {
                cnt--;
            }
            i++;
            
            if(cnt == 3) {
                result = max(result, j - i);
            }
        }
    }
    cout << result << endl;
    
    return 0;
}