long long quick_pow(int a,int n)  {      long long result;        if(n == 1) return a;      if(!n)    return 1;      long long mid = quick_pow(a,n/2);      if(n%2) result = mid*mid%modx*a%modx;      else    result = mid*mid%modx;      return result;  //zzzzz}