#include<bits/stdc++.h>
using namespace std;
using ll=long long;
using ld=long double;
using pll=pair<ll,ll>;
using plll=pair<ll,pll>;
using graph=vector<vector<int>>;
using wgraph=vector<vector<pll>>;

const ll MOD=1000000007;
const int dx[4]={1,0,-1,0};
const int dy[4]={0,1,0,-1};

ll abs1(ll a){
  if(a>=0)return a;
  else return -a;
}

ll pow1(ll a,ll b,ll p=LLONG_MAX){
  ll ret=1;
  while(b!=0){
    if((b&1)==1){
      ret*=a;
    }
    a*=a;
    if(a>=p)a%=p;
    b=b>>1;
  }
  return ret;
}

int digit(ll a,ll b){
  int i=0;
  while(a!=0){
    a/=b;
    i++;
  }
  return i;
}

ll gcd1(ll a,ll b){
  if(a==0 && b==0)return 0;
  ll n;
  while(a%b!=0){
    n=a%b;
    a=b;
    b=n;
  }
  return b;
}

ll solveLinear(ll n,ll m,ll c){
  if(n==0 && m==0)return 0;
  ll a[100],b[100];
  a[0]=n;b[0]=m;
  int i=1;
  while(b[i-1]!=0){
    a[i]=b[i-1];
    b[i]=a[i-1]%b[i-1];
    i++;
  }
  n=i;
  if(c%a[n-1]!=0){
    return 0;
  }
  ll x=c/a[n-1],y=0;
  for(i=1;i<n;i++){
    ll cnt=x;
    x=y;
    y=cnt-(a[n-i-1]/b[n-i-1])*y;
  }
  return x;
}

ll modRev(ll a,ll p=MOD){
  a%=p;
  ll n=solveLinear(a,p,1);
  n%=p;
  if(n<0)return n+p;
  return n;
}

ll fact(ll n,ll p=MOD){
  if(n<0)return 0;
  int i;
  ll ret=1;
  for(i=0;i<n;i++){
    ret=ret*(i+1);
    if(ret>=p)ret%=p;
  }
  return ret;
}

ll perm(ll n,ll k,ll p=MOD){
  if(n<0 || k<0 || n<k)return 0;
  int i;
  ll ret=1;
  for(i=0;i<k;i++){
    ret=ret*(n-i);
    if(ret>=p)ret%=p;
  }
  return ret;
}

ll binom(ll n,ll k,ll p=MOD){
  if(n<0 || k<0 || n<k)return 0;
  int i;
  ll ret=1,fact=1;
  for(i=0;i<k;i++){
    ret=ret*(n-i);
    fact*=i+1;
    if(ret>=p)ret%=p;
    if(fact>=p)fact%=p;
  }
  return (ret*modRev(fact))%p;
}

void pushHeap(vector<int>& h,int n){
  int i=h.size();
  h.push_back(n);
  while(i!=0 && h[(i-1)/2]<h[i]){
    swap(h[i],h[(i-1)/2]);
    i=(i-1)/2;
  }
  h[i]=n;
}

int popHeap(vector<int>& h){
  int n=h.size()-1;
  if(n==-1)return 0;
  int i,ret=h[0];
  swap(h[0],h[n]);
  h.pop_back();
  for(i=0;i<n;){
    int j=2*i+1;
    if(j>=n)break;
    if(j!=n-1 && h[j]<h[j+1])j++;
    if(h[i]<h[j]){
      swap(h[i],h[j]);
    }
    i=j;
  }
  return ret;
}

int bis(vector<int> v,int key){
  int left=-1,right=v.size();
  while(abs1(right-left)>1){
    int mid=left+(right-left)/2;
    if(v[mid]<=key)left=mid;
    else right=mid;
  }
  return left;
}

int main(){
  int i,j,k,cnt=0;
  int n;
  cin>>n;
  int d[n];
  for(i=0;i<n;i++)cin>>d[i];
  vector<int> b(13),p(24),q;
  for(i=1;i<=12;i++)b[i]=0;
  for(i=0;i<24;i++)p[i]=0;
  b[0]=1;p[0]=1;
  for(i=0;i<n;i++){
    b[d[i]]++;
  }
  if(b[0]>=2 || b[12]>=2){
    cout<<0<<endl;
    return 0;
  }
  vector<int> v;
  for(i=1;i<=11;i++){
    if(b[i]==1){
      v.push_back(i);
    }
    if(b[i]==2){
      p[i]=1;
      p[24-i]=1;
    }
    if(b[i]>=3){
      cout<<0<<endl;
      return 0;
    }
  }
  if(b[12]==1)p[12]=1;
  q=p;
  int t=pow1(2,v.size());
  int ma=0;
  for(i=0;i<t;i++){
    p=q;
    for(j=0;j<v.size();j++){
      if((i/pow1(2,j))%2==0)p[v[j]]++;
      else p[24-v[j]]++;
    }
    int mi=INT_MAX,cnt=0;
    for(j=1;j<24;j++){
      if(p[j]==1){
        mi=min(mi,j-cnt);
        cnt=j;
      }
      if(p[j]==2){
        mi=0;
      }
    }
    mi=min(mi,24-cnt);
    ma=max(ma,mi);
  }
  cout<<ma<<endl;
}


Measured memory_bytes: 256