#include <stdio.h>

int a,b,c,n,w;

int main() {
	
  FILE *f = fopen("nunta.in","r");
  FILE *g = fopen("nunta.out","w");
  
  fscanf(f,"%d",&n);

  a = 1;
  b = 2;
  w = 2;
  
  if (n > 2) {
    while (w < n) {
	  w++;
	  c = a+b;
	  a = b;
	  b = c;
    }	  
	fprintf(g,"%d",c);
  }
  else 
    if (n==1)
	  fprintf(g,"1");
	else
	  fprintf(g,"2");
  
  
  fclose(f);
  fclose(g);	
	
  return 0;
}