#include<stdio.h>
long a[50]={0,1,2};
int main()
{
int n,i;
while(scanf("%d",&n)==1)
{
for(i=3;i<=n;i++)
{
a[i]=a[i-1]+a[i-2];
}
printf("%ld\n",a[n]);
}
return 0;
}