#include<stdio.h>
unsigned long int K,N,aux;
int i;
int main()
{
	FILE *f = fopen("kfib.in","r");
	fscanf(f,"%lu",&K);
	fclose(f);
	
	if(K==1)
		N=0;
	else
		if(K==2)
			N=1;
		else
			if(K==3)
				N=1;
			else
			{
				aux=1;
				N=1;
				for(i=4;i<=K;i++)
				{
					aux=N;
					N=N+aux;
				}
			}
			
	FILE *g = fopen("kfib.out","w");
	fprintf(g,"%lu",N);
	fclose(g);
	return 0;
}