#include <algorithm>
#include <cassert>
#include <cstring>
#include <iostream>
#include <vector>

using namespace std;

#define FOR(i, a, b) for (int i = (a); i < (b); ++i)
#define REP(i, n) FOR(i, 0, n)
#define TRACE(x) cout << #x << " = " << x << endl
#define _ << " _ " <<

typedef long long llint;

const int MAX = 55;

vector<int> E[MAX];

bool bio[MAX];
int color[MAX];

bool dfs(int x, int col) {
  if (bio[x]) return color[x] == col;
  bio[x] = true;
  color[x] = col;
  for (int y: E[x]) {
    if (!dfs(y, col ^ 1)) return false;
  }
  return true;
}

int main(void) {
  int N;
  scanf("%d", &N);
  vector<int> d(N);
  REP(i, N) scanf("%d", &d[i]);

  auto can = [&] (int s) {
    REP(i, N) E[i].clear();
    REP(i, N) REP(j, i) {
      if (abs(d[i] - d[j]) < s) {
        int d2 = min(d[i] + d[j], 24 - (d[i] + d[j]));
        if (d2 < s) return false;
        E[i].push_back(j);
        E[j].push_back(i);
      }
    }

    REP(i, N) color[i] = 0, bio[i] = false;
    REP(i, N) if (!bio[i]) {
      if (!dfs(i, 0)) return false;
    }
    return true;
  };
  
  int ret = *min_element(d.begin(), d.end());
  while (!can(ret)) ret--;
  
  printf("%d\n", ret);
  return 0;
}
