#include<stdio.h>
unsigned long long int jump[10000];
void Climb(int n){
	int i;
	jump[1]=1;
	jump[2]=2;
	for(i=3;i<=n;i++){
		jump[i]=jump[i-1]+jump[i-2];
	}
} 
int main(){
	int n;
	//n为阶梯数
	scanf("%d",&n);
	Climb(n);
	printf("%llu",jump[n]);
}