#include<cstdio>
using namespace std;
int main()
{
    freopen("nunta.in","r",stdin);
    freopen("nunta.out","w",stdout);
    long long a,b,c;
    int n;
    a=1;b=2;
    scanf("%d",&n);
    if(n<=3) printf("%d",n);
    else
    {
        for(int i=1;i<=(n-2);i++)
            c=a;
        a=b;
        b=a+c;
        printf("%d",b);
    }
}