1193:吃糖果

//1193：吃糖果 
#include<cstdio>
using namespace std;
int main()
{
	int a[22];
	int n;
	scanf("%d",&n);
	a[1]=1;
	a[2]=2;
	for(int i=3;i<=20;++i)
	{
		a[i]=a[i-1]+a[i-2];	
	}
	printf("%d",a[n]);
	return 0;
}