#include<iostream>
using namespace std;
int main()
{
int a[25];
a[1] = 1;
a[2] = 2;
int n;
cin>>n;
if(n==1)
cout<<1<<endl;
else if(n==2)
cout<<2<<endl;
else
{
for(int i=3;i<=n;i++)
a[i] = a[i-1] + a[i-2];
cout<<a[n]<<endl;
}
return 0;
}