#include<stdio.h>
#include<stdlib.h>

typedef long long int ln;

int main(void){

	int N;
	scanf("%d",&N);

	ln a,b;
	a=1;
	b=1;
	while(N>1){
		ln c=a+b;
		a=b;
		b=c;
		N--;
	}

	printf("%lld\n",b);

	return 0;
}