class Algebra
  {
  static boolean isPrime(int c)     // Returns true if c is prime.
    {
    if (c % 2 == 0) return false;
    int d; d = 3;
    while (d != c)              // If c < 0 we're in trouble!
      {
      if (c % d == 0) return false;
      d = d + 2;
      }
    return true;
    } 
 
  static int gcd(int a, int b)  /* Find greatest common divisor. */
    {
    int m; m = b % a;
    if (m == 0)
      return a;
    else
      return gcd(m, a);
    }
  
  static int fibonacci(int n)   // Find n-th Fibonacci number.
    {
    if ((n == 1) || (n == 2))
      return 1;
    else 
      return fibonacci(n-1) + fibonacci(n-2);
    }
  }