#include<stdio.h>
int Fib(int n)
{
  int a = 1;
  int b = 1;
  int c = 1;
  while(n>2)
  {
  c = a+b;
  a = b;
  b = c;
  n--;
  }
  return c;
}
int main()
{
  int n=0;
  int ret = 0;
  scanf("%d",&n);
  ret = Fib(n);
  printf("ret = %d\n",ret);
  return 0;}