text: #include <stdio.h>
  #include <stdlib.h>
  #include <string.h>
  
  /*!
   * \brief Calculate Fibonacci Nth number
   *
   * Iterative implementation to calculate Fibonacci Nth number
   * \param[in] N Nth position in Fibonacci sequence N <= 90 (int)
   * \return Nth Fibonacci number (long)
   * */
  long calc_fib(int N) {
      if (N == 0) {
         return 0; 
      }
      long Fn, Fn1, temp;
      Fn = 1;
      Fn1 = temp = 0; 
      int i ;
      for ( i = 1; i <  N; ++i) {
          temp = Fn;
          Fn = Fn1 + Fn;
          Fn1 = temp;
      } 
      return Fn;
  }
  
  int main() {
      long n = 0;
      long fib;
      char buffer[100];
      fgets(buffer, 100, stdin);
      n = atoi(buffer);
      if (n > 90) {
          return -1;
      }
      fib = calc_fib(n);
      printf("%ld\n", fib); 
      return 0;
  }
  