#include<stdio.h>
int a1,a2,i,s,n,k;
int main()
{
freopen("kfib.in","r",stdin);
freopen("kfib.out","w",stdout);
scanf("%d",&k);
a1=1;
a2=2;
for(i=3;i<=k;i++)
    {s=a1+a2;
    a1=a2;
    a2=s;
    }
printf("%d",a1);
return 0;
}