using System;

class Fibonacci {
  static void Main() {
    int n, i, Fn, Fn_1, Fn_2;
    Console.WriteLine("Unesi n");
    n = int.Parse(Console.ReadLine());
    if(n <= 0) { Console.WriteLine("Nije definisan"); }
    else if (n == 1 || n == 2) { Console.WriteLine("F_n = 1"); }
    else {
      Fn_1 = 1;
      Fn = 1;
      for(i = 3; i <= n; i++) {
        Fn_2 = Fn_1;
        Fn_1 = Fn;
        Fn = Fn_1 + Fn_2;
      }
      Console.WriteLine("F_n = {0}", Fn);
    }
  }
}