#include<stdio.h>

int N;
unsigned long long a = 1;
unsigned long long b = 1;
unsigned long long c;

int main()
{
	FILE *f = fopen("nunta.in","r");
	FILE *g = fopen("nunta.out","w");
	
	fscanf(f,"%d",&N);
	for(int i=2;i<=N;i++)
	{
		c = a+b;
		a = b;
		b = c;
	}
	fprintf(g,"%llu",c);
		
	fclose(g);
	fclose(f);
	return 0;
}