#include <iostream>
using namespace std;
#define FAIL { cout << "0\n"; return 0; }
#define active(i,k) ((i)&(1<<(k)))

int main() {
    int N, t, a[24] = {}, i;
    cin >> N;
    a[0] = 1;
    for (i = 0; i < N; i++) {
        cin >> t;
        if (a[t]) {
            t = (24-t)%24;
            if (a[t]) FAIL;
        }
        a[t]++;
    }

    int R = 0;
    for (i = 0; i < 4096; i++) {
        int j = 0, k = 1, r = 24;

        for (int l = 1; l < 12; l++) {
            // if a[l] is inverted and a[24-l] exists
            if (active(i, l) && a[24-l]) r = 0;
        }

        // find next k that is ACTIVATED
        while (k < 24) {
            // k is activated if:
            // + k >= 12: a[k] exists OR inverted is active
            // + k < 12: a[k] exists AND not inverted

            for (;k < 24; k++) {
                if (k >= 12) {
                    if (a[k] || (a[24-k] && active(i, 24-k))) break;
                } else {
                    if (a[k] && !active(i, k)) break;
                }
            }
            if (k == 24) break;

            //printf("j,k: %d, %d\n", j, k);
            r = min(r, k-j);
            j = k++;
        }

        // check end
        r = min(r, 24-j);
        //printf("%d: %d\n", i, r);
        R = max(R, r);
    }
    cout << R << '\n';


}